Prosthetic intervertebral discs having substantially rigid end plates and fibers between those end plates

ABSTRACT

Prosthetic intervertebral discs and methods for using the same are described. The subject prosthetic discs include upper and lower endplates separated by a compressible core member. The prosthetic discs described herein include one-piece, two-piece, three-piece, and four-piece structures. The subject prosthetic discs exhibit stiffness in the vertical direction, torsional stiffness, bending stiffness in the saggital plane, and bending stiffness in the front plane, where the degree of these features can be controlled independently by adjusting the components of the discs. The interface mechanism between the endplates and the core members of several embodiments of the described prosthetic discs enables a very easy surgical operation for implantation.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/903,276,filed Jul. 30, 2004, which in turn, is a continuation-in-part ofco-pending application Ser. No. 10/632,538, filed Aug. 1, 2003, whichprior applications are incorporated by reference.

BACKGROUND OF THE INVENTION

The intervertebral disc is an anatomically and functionally complexjoint. The intervertebral disc is composed of three componentstructures: (1) the nucleus pulposus; (2) the annulus fibrosus; and (3)the vertebral endplates. The biomedical composition and anatomicalarrangements within these component structures are related to thebiomechanical function of the disc.

The spinal disc may be displaced or damaged due to trauma or a diseaseprocess. If displacement or damage occurs, the nucleus pulposus mayherniate and protrude into the vertebral canal or intervertebralforamen. Such deformation is known as herniated or slipped disc. Aherniated or slipped disc may press upon the spinal nerve that exits thevertebral canal through the partially obstructed foramen, causing painor paralysis in the area of its distribution.

To alleviate this condition, it may be necessary to remove the involveddisc surgically and fuse the two adjacent vertebra. In this procedure, aspacer is inserted in the place originally occupied by the disc and itis secured between the neighboring vertebrae by the screws andplates/rods attached to the vertebra. Despite the excellent short-termresults of such a “spinal fusion” for traumatic and degenerative spinaldisorders, long-term studies have shown that alteration of thebiomechanical environment leads to degenerative changes at adjacentmobile segments. The adjacent discs have increased motion and stress dueto the increased stiffness of the fused segment. In the long term, thischange in the mechanics of the motion of the spine causes these adjacentdiscs to degenerate.

To circumvent this problem, an artificial intervertebral discreplacement has been proposed as an alternative approach to spinalfusion. Although various types of artificial intervertebral discs havebeen developed to restore the normal kinematics and load-sharingproperties of the natural intervertebral disc, they can be grouped intotwo categories, i.e., ball and socket joint type discs and elasticrubber type discs.

Artificial discs of ball and socket type are usually composed of metalplates, one to be attached to the upper vertebra and the other to beattached to the lower vertebra, and a polyethylene core working as aball. The metal plates have concave areas to house the polyethylenecore. The ball and socket type allows free rotation between thevertebrae between which the disc is installed and thus has no loadsharing capability against the bending. Artificial discs of this typehave a very high stiffness in the vertical direction, they cannotreplicate the normal compressive stiffness of the natural disc. Also,the lack of load bearing capability in these types of discs causesadjacent discs to take up the extra loads resulting in the eventualdegeneration of the adjacent discs.

In elastic rubber type artificial discs, an elastomeric polymer isembedded between metal plates and these metal plates are fixed to theupper and the lower vertebrae. The elastomeric polymer is bonded to themetal plates by having the interface surface of the metal plates berough and porous. This type of disc can absorb a shock in the verticaldirection and has a load bearing capability. However, this structure hasa problem in the interface between the elastomeric polymer and the metalplates. Even though the interface surfaces of the metal plates aretreated for better bonding, polymeric debris may nonetheless begenerated after long term usage. Furthermore, the elastomer tends torupture after a long usage because of its insufficient shear-fatiguestrength.

Because of the above described disadvantages associated with either theball/socket or elastic rubber type discs, there is a continued need forthe development of new prosthetic devices.

RELEVANT LITERATURE

U.S. Pat. Nos. 3,867,728; 4,911,718; 5,039,549; 5,171,281; 5,221,431;5,221,432; 5,370,697; 5,545,229; 5,674,296; 6,162,252; 6,264,695;6,533,818; 6,582,466; 6,582,468; 6,626,943; 6,645,248. Also of interestare published U.S. Patent Application Nos. 2002/0107575, 2003/0040800,2003/0045939, and 2003/0045940. See also Masahikio Takahata, UasuoShikinami, Akio Minami, “Bone Ingrowth Fixation of ArtificialIntervertebral Disc Consisting of Bioceramic-Coated Three-dimensionalFabric,” SPINE, Vol. 28, No. 7, pp. 637-44 (2003).

SUMMARY OF THE INVENTION

Prosthetic intervertebral discs and methods for using such discs areprovided. The subject prosthetic discs include an upper endplate, alower endplate, and a compressible core member disposed between the twoendplates.

In one embodiment, the subject prosthetic discs are characterized byincluding top and bottom endplates separated by a fibrous compressibleelement that includes an annular region and a nuclear region. The twoplates are held together by at least one fiber wound around at least oneregion of the top endplate and at least one region of the bottomendplate. The subject discs may be employed with separate vertebral bodyfixation elements, or they may include integrated vertebral bodyfixation elements. Also provided are kits and systems that include thesubject prosthetic discs.

In other embodiments, the prosthetic disc comprises an integrated,single-piece structure. In another embodiment, the prosthetic disccomprises a two-piece structure including a lower endplate and aseparable upper endplate assembly that incorporates the core member. Thetwo-piece structure may be a constrained structure, wherein the upperendplate assembly is attached to the lower endplate in a manner thatprevents relative rotation, or a partially or semi-constrained structureor an unconstrained structure, wherein the upper endplate assembly isattached to the lower endplate in a manner that allows relativerotation. In yet another, embodiment, the prosthetic disc comprises athree-piece structure including upper and lower endplates and aseparable core member that is captured between the upper and lowerendplates by a retaining mechanism. Finally, in yet another embodiment,the prosthetic disc comprises a four-piece structure including upper andlower endplates and two separable core assemblies which, together, forma core member.

Several optional core materials and structures may be incorporated ineach of the prosthetic disc embodiments described herein. For example,the core member may be formed of a relatively compliant material, suchas polyurethane or silicone, and is typically fabricated by injectionmolding. In other examples, the core member may be formed by layers offabric woven from fibers. In still further examples, the core member maycomprise a combination of these materials, such as a fiber-reinforcedpolyurethane or silicone. As an additional option, one or more springmembers may be placed between the upper and lower endplates incombination with the core member, such as in a coaxial relationship inwhich the core member has a generally cylindrical or toroidal shape anda spring is located at its center.

In the various embodiments, the disc structures are held together by atleast one fiber wound around at least one region of the upper endplateand at least one region of the lower endplate. The fibers are generallyhigh tenacity fibers with a high modulus of elasticity. The elasticproperties of the fibers, as well as factors such as the number offibers used, the thickness of the fibers, the number of layers of fiberwindings, the tension applied to each layer, and the crossing pattern ofthe fiber windings enable the prosthetic disc structure to mimic thefunctional characteristics and biomechanics of a normal-functioning,natural disc.

Apparatus and methods for implanting prosthetic intervertebral discs arealso provided. In a first embodiment, the apparatus includes threeimplantation tools used to prepare the two adjacent vertebral bodies forimplantation and then to implant the prosthetic disc. A first tool, aspacer, is adapted to be inserted between and to separate the twoadjacent vertebral bodies to create sufficient space for implanting theprosthetic disc. A second tool, a chisel, includes one or morewedge-shaped cutting blades located on its upper and/or lower surfacesthat are adapted to create grooves in the inward facing surfaces of thetwo adjacent vertebral bodies. A third tool, a holder, includes anengagement mechanism adapted to hold the prosthetic disc in place whileit is being implanted, and to release the disc once it has beenimplanted.

In another embodiment, the implantation apparatus includes a guidemember that engages the lower endplate and that remains in place duringa portion of the disc implantation process. A lower pusher memberslidably engages the guide member and is used to advance the lowerendplate into place between two adjacent vertebrae of a patient's spine.An upper pusher member is preferably coupled to the lower pusher memberand is used to advance a first chisel into place opposed to the lowerendplate between the two adjacent vertebrae. Once in place, an upwardforce is applied to the upper pusher member to cause the first chisel toengage the upper vertebral body and to create one or more grooves on itslower surface. A downward force is also applied to the lower pushermember to cause the lower endplate to engage the lower vertebral bodyand to become implanted. The upper pusher member and first chisel arethen removed, as is the lower pusher member. Preferably, a second chiselis then advanced along the guide member and is used to provideadditional preparation of the upper vertebral body. After the completionof the preparation by the first chisel and, preferably, the secondchisel, the upper endplate and core members of the prosthetic disc areimplanted using an upper endplate holder that is advanced along theguide member. After implantation, the upper endplate holder and guidemember are removed.

Apparatus and methods for implanting prosthetic intervertebral discsusing minimally invasive surgical procedures are also provided. In oneembodiment, the apparatus includes a pair of cannulas that are insertedposteriorly, side-by-side, to gain access to the spinal column at thedisc space. A pair of prosthetic discs are implanted by way of thecannulas to be located between two vertebral bodies in the spinalcolumn. In another embodiment, a single, selectively expandable disc isemployed. In an unexpanded state, the disc has a relatively smallprofile to facilitate delivery of it to the disc space. Once Operativelypositioned, it can then be selectively expanded to an appropriate sizeto adequately occupy the disc space. Implantation of the single discinvolves use of a single cannula and an articulating chisel or a chiselotherwise configured to establish a curved or right angle disc deliverypath so that the disc is substantially centrally positioned in the discspace. Preferably, the prosthetic discs have sizes and structuresparticularly adapted for implantation by the minimally invasiveprocedure.

Other and additional devices, apparatus, structures, and methods aredescribed by reference to the drawings and detailed descriptions below.

DESCRIPTION OF THE DRAWINGS

The Figures contained herein are not necessarily drawn to scale, withsome components and features being exaggerated for clarity.

FIGS. 1A and 1B provide a three dimensional view of two differentprosthetic discs according to the subject invention.

FIG. 2 provides a three-dimensional view of a fibrous compressibleelement that includes a polymeric nucleus and a fibrous annulusaccording to one embodiment of the subject invention.

FIGS. 3A to 3C provide different views of a fibrous component of thefibrous compressible elements according to an embodiment of the subjectinvention. FIG. 3C illustrates the manner in which the 2D fabrics inFIG. 3B are stitched together.

FIG. 4A provides a three-dimensional top view of a prosthetic discaccording to an embodiment of the present invention in which thefixation elements are integral to the disc, while FIG. 4B shows the discof FIG. 4A implanted with the use of bone screws.

FIGS. 5A and 5B show the mating interface between disc top endplate withan upper vertebral body fixation element according to an embodiment ofthe subject invention.

FIGS. 6A and 6B show the mating interface between disc top endplate withan upper vertebral body fixation element according to an alternativeembodiment of the subject invention. The top endplate is clamped by aclamping element connected to the upper vertebral body fixation elementthrough a spring.

FIG. 7 provides an exploded view of a disc system that includes both anintervertebral disc and vertebral body fixation elements, according toan embodiment of the present invention.

FIGS. 8 and 9 provide views of vertebral body fixation elements beingheld in an implantation device according to an embodiment of the subjectinvention.

FIG. 10 provides a view of disc implantation device and disc accordingto an embodiment of the subject invention.

FIG. 11 provides sequential views of a disc being replaced with aprosthetic disc according to a method of the subject invention.

FIG. 12 provides a cross-sectional view of a prosthetic disc having aone-piece structure.

FIG. 13A provides a three-dimensional view of a prosthetic disc having aone-piece structure including a single anchoring fin on each of theupper and lower endplates.

FIG. 13B provides a three-dimensional view of a prosthetic disc having aone-piece structure including three anchoring fins on each of the upperand lower endplates.

FIG. 13C provides a three-dimensional view of a prosthetic disc having aone-piece structure including a serrated surface on each of the upperand lower endplates.

FIG. 13D provides a three-dimensional view of a prosthetic disc having aone-piece structure including a superior dome.

FIG. 13E provides a three-dimensional view of the prosthetic disc havinga one-piece structure of FIG. 13D, having no superior dome.

FIG. 13F provides a three-dimensional cross-sectional view of theprosthetic disc having a one-piece structure shown in FIG. 13D.

FIG. 13G provides a three-dimensional view of a prosthetic disc having aprosthetic structure design without a gasket retaining ring.

FIG. 13H provides a three-dimensional cross-sectional view of theprosthetic disc having a one-piece structure shown in FIG. 2G.

FIG. 13I provides a cross-sectional view of an upper endplate of aprosthetic disc having a one-piece structure design without a gasketretaining ring.

FIG. 13J provides an inset view of a portion of the upper endplate shownin FIG. 2I.

FIG. 13K provides a cross-sectional illustration of a prosthetic dischaving a one-piece structure design with a center spring.

FIG. 13L provides a three-dimensional cross-sectional illustration ofthe prosthetic disc having a one-piece structure shown in FIG. 13K.

FIGS. 14A and B provide illustrations of uni-directional andbi-directional fiber winding patterns.

FIGS. 15A-C provide illustrations of an annular capsule.

FIG. 16 provides a three-dimensional view of a prosthetic disc having atwo-piece structure.

FIG. 17 provides a three-dimensional view of an outer lower endplate ofthe prosthetic disc shown in FIG. 16.

FIG. 18 provides a cross-sectional view of a prosthetic disc having atwo-piece constrained structure.

FIG. 19 provides a three-dimensional view of a prosthetic disc having atwo-piece unconstrained structure.

FIG. 20 provides a cross-sectional view of a prosthetic disc having atwo-piece constrained structure.

FIG. 21 provides a three-dimensional view of a prosthetic disc having athree-piece structure.

FIG. 22 provides a three-dimensional view of a lower endplate of theprosthetic disc shown in FIG. 21.

FIG. 23 provides a cross-sectional view of a prosthetic disc having athree-piece structure.

FIG. 24A provides a three-dimensional view of a core assembly for aprosthetic disc having a three-piece structure.

FIG. 24B provides a three-dimensional view of another core assembly fora prosthetic disc having a three-piece structure.

FIG. 24C provides a three-dimensional view of another core assembly fora prosthetic disc having a three-piece structure.

FIG. 25A provides a cross-section view of a fiber reinforced coreassembly.

FIG. 25B provides a cross-section view of another fiber reinforced coreassembly.

FIG. 25C provides a cross-section view of another fiber reinforced coreassembly.

FIG. 26 provides a three-dimensional view of a stacked fabric coreassembly.

FIG. 27 provides a cross-sectional view of a stacked fabric coreassembly.

FIG. 28A provides a three-dimensional view of a stacked fabric coreassembly.

FIG. 28B provides a three-dimensional view of another stacked fabriccore assemble.

FIG. 28C provides a three-dimensional view of another stacked fabriccore assemble.

FIG. 29 provides a three-dimensional view of a prosthetic disc having afour-piece structure.

FIG. 30 provides a cross-sectional view of a prosthetic disc having afour-piece structure.

FIG. 31 provides an expanded view of a core assembly for a prostheticdisc having a four-piece structure.

FIG. 32 provides a three-dimensional view of a prosthetic disc having afour-piece structure.

FIG. 33 provides a cross-sectional view of a prosthetic disc having afour-piece structure.

FIG. 34 provides a three-dimensional view of a prosthetic disc having afour-piece structure.

FIG. 35 provides an expanded view of a core assembly for a prostheticdisc having a four-piece structure.

FIG. 36A provides a perspective view of a spacer.

FIG. 36B provides a perspective view of the head portion of the spacershown in FIG. 36A.

FIG. 37A provides a perspective view of a double-sided chisel.

FIG. 37B provides a top view of the head portion of the double-sidedchisel shown in FIG. 37A.

FIG. 38A provides a perspective view of a holder.

FIG. 38B provides a perspective view of the head portion of the holdershown in FIG. 38A.

FIG. 39 provides a perspective view of a guide member.

FIG. 40 provides a perspective view of a first chisel and lower endplateinsert apparatus.

FIG. 41 provides a perspective view of an upper endplate holder.

FIG. 42 provides a perspective view of a second chisel.

FIG. 43A provides an illustration of a method step of advancing a firstchisel and outer lower endplate.

FIG. 43B provides an illustration showing a pair of adjacent vertebraeduring an implantation procedure.

FIG. 44A provides an illustration of a method step of providing a forceseparating a first chisel and an outer lower endplate.

FIG. 44B provides an illustration of a pair of adjacent vertebrae duringthe method step shown in FIG. 44A.

FIG. 45A provides an illustration of a guide member and outer lowerendplate.

FIG. 45B provides an illustration of a pair of vertebrae with an outerlower endplate implanted onto the lower vertebra.

FIG. 46A provides an illustration of a method step of advancing a secondchisel.

FIG. 46B provides an illustration of a pair of adjacent vertebrae duringthe method step shown in FIG. 46A.

FIG. 47A provides an illustration of a guide member and outer lowerendplate.

FIG. 47B provides an illustration of a pair of vertebrae with an outerlower endplate implanted onto the lower vertebra.

FIG. 48A provides an illustration of a method step of advancing aprosthetic disc upper subassembly.

FIG. 48B provides an illustration of a pair of adjacent vertebrae duringthe method step shown in FIG. 48A.

FIG. 49A provides an illustration of a method step of withdrawing anupper endplate holder and guide member.

FIG. 49B provides an illustration of a pair of vertebrae with aprosthetic disc having been implanted therebetween.

FIG. 50A provides a three-dimensional view of a preferred prostheticdisc for use with a minimally invasive surgical procedure.

FIG. 50B provides a three-dimensional view of another preferredprosthetic disc for use with a minimally invasive surgical procedure.

FIG. 51 provides an illustration of a minimally invasive surgicalprocedure for implanting a pair of prosthetic discs.

FIG. 52A provides an illustration of an alternative minimally invasivesurgical procedure for implanting a prosthetic disc.

FIG. 52B provides a schematic illustration of a dual prosthetic dischaving a mechanism for separating the discs after implantation.

FIG. 53 provides a cross-sectional schematic illustration of ananti-creep compression member.

FIG. 54 provides a cross-sectional illustration of a mechanism fordeploying and retracting fins and/or spikes located on prosthetic discendplate.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Before the present invention is described, it is to be understood thatthis invention is not limited to particular embodiments described, assuch may, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting, since the scope ofthe present invention will be limited only by the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges is also encompassed within the invention, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either or both ofthose included limits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present invention, the preferredmethods and materials are now described. All publications mentionedherein are incorporated herein by reference to disclose and describe themethods and/or materials in connection with which the publications arecited.

It must be noted that as used herein and in the appended claims, thesingulars forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentinventions.

Prosthetic intervertebral discs, methods of using such discs, apparatusfor implanting such discs, and methods for implanting such discs aredescribed herein. It is to be understood that the prostheticintervertebral discs, implantation apparatus, and methods are notlimited to the particular embodiments described, as these may, ofcourse, vary. It is also to be understood that the terminology usedherein is for the purpose of describing particular embodiments only, andis not intended to be limiting, since the scope of the presentinventions will be limited only by the appended claims.

The following description includes three Parts. Part A contains adescription of a first set of embodiments of the subject prostheticintervertebral discs, a review of representative methods for using theprosthetic discs, and a review of systems and kits that include thesubject prosthetic discs. The embodiments described in Part A are thoseillustrated in FIGS. 1-11. Part B contains a description of a second setof embodiments of the subject prosthetic intervertebral discs, methodsfor using the discs, and apparatus and methods for implanting the discs.The embodiments described in Part B are those illustrated in FIGS.12-54. Each of the descriptions contained in Parts A and B will beunderstood to be complete and comprehensive in its own right, as well asdescribing structures, features, and methods that are suitable for usewith those described in the other Part. Part C includes additionalinformation about the descriptions contained herein.

Part A

I. Prosthetic Intervertebral Disc

As summarized above, the subject invention is directed to a prostheticintervertebral disc. By prosthetic intervertebral disc is meant anartificial or manmade device that is configured or shaped so that it canbe employed as a replacement for an intervertebral disc in the spine ofa vertebrate organism, e.g., a mammal, such as a human. The subjectprosthetic intervertebral disc has dimensions that permit it tosubstantially occupy the space between two adjacent vertebral bodiesthat is present when the naturally occurring disc between the twoadjacent bodies is removed, i.e., a void disc space. By substantiallyoccupy is meant that it occupies at least about 75% by volume, such asat least about 80% by volume or more. The subject discs may have aroughly bean shaped structure analogous to naturally occurringintervertebral body discs which they are designed to replace. In manyembodiments the length of the disc ranges from about 15 mm to about 50mm, such as from about 18 mm to about 46 mm, the width of the discranges from about 12 mm to about 30 mm, such as from about 14 mm toabout 25 mm and the height of the disc ranges from about 3 mm to about13 mm, such as from about 5 mm to about 12 mm.

The subject discs are characterized in that they include both an upper(or top) and lower (or bottom) endplate, where the upper and lowerendplates are separated from each other by a fibrous compressibleelement, where the combination structure of the endplates and fibrouscompressible element provides a prosthetic disc that functionallyclosely mimics real disc. A feature of the subject prosthetic discs isthat the top and bottom endplates are held together by at least onefiber, e.g., of the fibrous compressible element, wound around at leastone portion of each of the top and bottom endplates. As such, the twoendplates (or planar substrates) are held to each other by one or morefibers that are wrapped around at least one domain/portion/area of theupper endplate and lower endplate such that the plates are joined toeach other.

Two different representative intervertebral discs are shown in FIGS. 1Aand 1B. As can be seen in FIGS. 1A and 1B, prosthetic discs 10 eachinclude a top endplate 11 and a lower endplate 12. Top and bottomendplates 11 and 12 are planar substrates, where these plates typicallyhave a length from about 12 mm to about 45 mm, such as from about 13 mmto about 44 mm, a width of from about 11 mm to about 28 mm, such as fromabout 12 mm to about 25 mm and a thickness of from about 0.5 mm to about4 mm, such as from about 1 mm to about 3 mm. The top and bottomendplates are fabricated from a physiologically acceptable material thatprovides for the requisite mechanical properties, where representativematerials from which the endplates may be fabricated are known to thoseof skill in the art and include, but are not limited to: titanium,titanium alloys, stainless steel, cobalt/chromium, etc.; plastics suchas polyethylene with ultra high molar mass (molecular weight) (UHMW-PE),polyether ether ketone (PEEK), etc.; ceramics; graphite; etc. As shownin FIGS. 1A and 1B, separating the top and bottom endplates is a fibrouscompressible element 17. The thickness of the fibrous compressibleelement may vary, but ranges in many embodiments from about 2 mm toabout 10 mm, including from about 3 mm to about 8 mm.

The disc is further characterized in that it includes an annular region13 (i.e., annulus), which is the region, domain or area that extendsaround the periphery of the disc, and a nuclear region (i.e., nucleus)14, which is the region, domain or area in the center of the disc andsurrounded by the annulus.

While in the broadest sense the plates may include a single regionaround which a fiber is wound in order to hold the plates together, inmany embodiments the plates have a plurality of such regions. As shownin FIGS. 1A and 1B, endplates 111 and 12 include a plurality of slots 15through which fibers, e.g., of the fibrous compressible element, may bepassed through or wound, as shown. In many embodiments, the number ofdifferent slots present in the periphery of the device ranges from about4 to about 36, such as from about 5 to about 25. As shown in FIGS. 1Aand 1B, at least one fiber 16 of the fibrous compressible element iswrapped around a region of the top and bottom plates, e.g., by beingpassed through slots in the top and bottom plates, in order to hold theplates together.

The fibrous compressible elements, 17, are typically made up of one ormore fibers, where the fibers are generally high tenacity fibers with ahigh modulus of elasticity. By high tenacity fibers is meant fibers thatcan withstand a longitudinal stress without tearing asunder of at leastabout 50 MPa, such as at least about 250 MPa. As the fibers have a highmodulus of elasticity, their modulus of elasticity is typically at leastabout 100 MPa, usually at least about 500 MPa. The fibers are generallyelongate fibers having a diameter that ranges from about 3 mm to about 8mm, such as about 4 mm to about 7 mm, where the length of eachindividual fiber making up the fibrous component may range from about 1m to about 20 m, such as from about 2 m to about 15 m.

The fibers making up the fibrous compressible elements may be fabricatedfrom any suitable material, where representative materials of interestinclude, but are not limited to: polyester (e.g., Dacron), polyethylene,polyaramid, carbon or glass fibers, polyethylene terephthalate, acrylicpolymers, methacrylic polymers, polyurethane, polyurea, polyolefin,halogenated polyolefin, polysaccharide, vinylic polymer,polyphosphazene, polysiloxane, and the like.

The fibrous compressible elements made up of one or more fibers woundaround one or more regions of the top or bottom plates may make up avariety of different configurations. For example, the fibers may bewound in a pattern that has an oblique orientation to simulate theannulus of intact disc, where a representative oblique fiberconfiguration or orientation is shown in FIG. 1A. The number of layersof fiber winding may be varied to achieve similar mechanical propertiesto an intact disk. Where desired, compliancy of the structure may bereduced by including a horizontal winding configuration, as shown inFIG. 1B.

In certain embodiments, the fibrous compressible element 20 has afibrous component 21 limited to the annular region of the disc 22, e.g.,to the region along the periphery of the disc. FIG. 2 provides arepresentation of this embodiment, where the fibrous component islimited solely to the annular region of the disc and includes bothoblique and horizontal windings. Also shown is a separate polymericcomponent 23 present in the nucleus. The fiber windings of the variouslayers of fiber may be at varying angles from each other where theparticular angle for each layer may be selected to provide aconfiguration that best mimics the natural disc. Additionally, thetension placed on the fibers of each layer may be the same or varied.

In yet other embodiments the fibrous component of the fibrouscompressible element may extend beyond the annular region of the discinto at least about a portion, if not all, of the nucleus. FIG. 3Aprovides a view of a fibrous component 30 that occupies both the annularand nuclear regions of the disc, where the annular region of the disc ismade up of fiber windings that are both oblique and horizontal, asdescribed above, while the nucleus of the disc is occupied by fiberswoven into a three-dimensional network that occupies the nuclear space.Instead of a three-dimensional network structure, one may have multipletwo dimensional layers' of interwoven fibers stacked on top of eachother, as shown in FIG. 3B, where the multiple stacked layers may bestitched to each other, as shown in FIG. 3C. By adjusting one or moreparameters of the fibrous component, such as the density of the fibers,number of layers, frequency of stitching, the wrapping angle of eachfiber layer, and the like, the mechanical properties of the fibrouscomponent can be tailored as desired, e.g., to mimic the mechanicalproperties of a natural intervertebral disc. Also shown in FIGS. 3B and3C is the outline of a polymeric component 32 in which the fibrouscomponent 30 is embedded.

In certain embodiments, the fibrous compressible element furtherincludes one or more polymeric components. The polymeric component(s),when present, may be fabricated from a variety of differentphysiologically acceptable materials. Representative materials ofinterest include, but are not limited to: elastomeric materials, such aspolysiloxane, polyurethane, poly(ethylene propylene) copolymer,polyvinylchloride, poly(tetrafluoro ethylene) and copolymers, hydrogels,and the like.

The polymeric component may be limited to particular domains, e.g., theannular and/or nucleus domains, or extend throughout the entire regionof the fibrous compressible elements positioned between the twoendplates. As such, in certain embodiments the polymeric component isone that is limited to the nuclear region of the disc, as shown in FIG.2. In FIG. 2, fibrous compressible element 20 includes a distinctfibrous component 21 that is located in the annular region of the disc22, while polymeric component 23 is located in the nuclear region of thedisc. In other embodiments, the polymeric component is located in boththe annular and nuclear regions. In yet other embodiments, the polymericcomponent may be located solely in the annular region.

Depending on the desired configuration and mechanical properties, thepolymeric component may be integrated with the fibrous component, suchthat at least a portion of the fibers of the fibrous component isembedded in, e.g., complexed with, at least a portion of the polymericcomponent. In other words, at least a portion of the fibrous componentis impregnated with at least a portion of the polymeric component. Forexample, as shown in FIG. 3B, stacked two-dimensional layers of thefibrous component 30 are present inside the polymeric component 32, suchthat the fibrous component is impregnated with the polymeric component.

In those configurations where the fibrous and polymeric components arepresent in a combined format, e.g., as shown in FIG. 3B, the fibers ofthe fibrous component may be treated to provide for improved bondingwith the polymeric component. Representative fiber treatments ofinterest include, but are not limited to: corona discharge, O₂ plasmatreatment, oxidation by strong acid (HNO₃, H₂SO₄). In addition, surfacecoupling agents may be employed, and/or a monomer mixture of the polymermay be polymerized in presence of the surface-modified fiber to producethe composite fiber/polymeric structure.

As indicated above, the devices may include one or more differentpolymeric components. In those embodiments where two or more differentpolymeric components are present, any two given polymeric components areconsidered different if they differ from each other in terms of at leastone aspect, e.g., composition, cross-linking density, and the like. Assuch, the two or more different polymeric components may be fabricatedfrom the same polymeric molecules, but differ from each other in termsof one or more of: cross-linking density; fillers; etc. For example, thesame polymeric material may be present in both the annulus and nucleusof the disc, but the crosslink density of the annulus polymericcomponent may be higher than that of the nuclear region. In yet otherembodiments, polymeric materials that differ from each other withrespect to the polymeric molecules from which they are made may beemployed.

By selecting particular fibrous component and polymeric componentmaterials and configurations, e.g., from the different representativeformats described above, a disc with desired functional characteristics,e.g., that mimics the functional characteristics of the naturallyoccurring disc, may be produced.

Representative particular combinations of interest include, but are notlimited to, the following:

-   -   1. Biocompatible polyurethane, such as Ethicon Biomer,        reinforced with Dacron poly(ethylene terephthalate) fiber, or        Spectra polyethylene fiber, or Kevlar polyaramide fiber, or        carbon fiber.    -   2. Biocompatible polysiloxane modified styrene-ethylene butylene        block copolymer sold under C-Flex tradename reinforced with        Dacron poly(ethylene terephthalate) fiber, or Spectra        polyethylene fiber, or Kevlar polyaramide fiber, or carbon        fiber.    -   3. Biocompatible Silastic silicone rubber, reinforced with        Dacron poly(ethylene terephthalate) fiber, or Spectra        polyethylene fiber, or Kevlar polyaramide fiber, or carbon        fiber.

In using the subject discs, the prosthetic disc is fixed to thevertebral bodies between which it is placed. More specifically, theupper and lower plates of the subject discs are fixed to the vertebralbody to which they are adjacent. As such, the subject discs are employedwith vertebral body fixation elements during use. In certainembodiments, the vertebral body fixation elements are integral to thedisc structure, while in other embodiments the vertebral body fixationelements are separate from the disc structure.

A representative embodiment of those devices where the vertebral bodyfixation elements are integral with the disc structure is depicted inFIGS. 4A and 4B. FIG. 4A shows device 40 made up of top and bottomendplates 41 and 42. Integrated with top and bottom endplates 41 and 42are vertebral body fixation elements 43 and 44. The vertebral bodyfixation elements include holes through which bone screws may be passedfor fixation of the disc to upper and lower vertebral bodies 47 and 48upon implantation, as represented in FIG. 4B.

In an alternative embodiment, the disc does not include integratedvertebral body fixation elements, but is designed to mate with separatevertebral body fixation elements, e.g., as depicted in FIG. 7. In otherwords, the disc is structured to interface with separate vertebral bodyfixation elements during use. Any convenient separate vertebral bodyfixation element may be employed in such embodiments, so long as itstably positions the prosthetic disc between two adjacent vertebralbodies.

One representative non-integrated vertebral body fixation elementaccording to this embodiment is shown in FIGS. 5A and 5B. FIG. 5Aprovides a representation of the upper plate 50 of a prosthetic discmated with a vertebral body fixation element 51, as the structures wouldappear upon implantation. Vertebral body fixation element 51 is ahorseshoe shaped structure having spikes 55 at locations correspondingto the cortical bone of vertebrae and porous coating to enhance bonefixation. The fixation element 51 also has gear teeth 52 such thatcorresponding gear teeth 53 of the disc upperplate 50 can slide throughthe gear contact resulting in the right location of prosthetic disc withrespect to the fixation element. The gear teeth have a shape such thatonly inward movement of the upper plate upon implantation is possible.Also present are slots 56 in the spiked fixation elements next to thegear teeth that provide for the elastic deformation of the whole teetharea upon implantation and desirable clearance between mating gear teethof the disc and fixation element so that incoming gear teeth of the disccan easily slide into the fixation element.

In the embodiment shown in FIG. 5A, as the disc is pushed into thefixation element, the protruded rail 57 on the disc slides along thecorresponding concave rail-way 58 on the fixation element until theprotruded rail on the most front side is pushed into the correspondingconcave rail-way on the fixation element, as shown in FIG. 5B. This railinterface is devised to prevent the upward/downward movement of the topdisc endplate and the bottom disc endplate with respect to thecorresponding fixation element. This interface between the fixationelements and the top and bottom endplates of the disc enables an easysurgical operation. Specifically, the fixation elements are transferredtogether to the disc replacement area (disc void space) with aninstrument and pushed in the opposite directions toward the vertebraeuntil they are fixed to the vertebrae, and then the prosthetic disc istransferred by the instrument between the fixation elements and simplypushed inward until the stoppers mate the corresponding stoppers. Theprosthetic disc can also be easily removed after long-term use. For itsremoval, the gear teeth on the fixation element are pushed to reduce thegap of the slot so that the gear engagement between the disc endplateand the fixation element is released.

An alternative embodiment is depicted in FIGS. 6A and 6B. In theembodiment shown in FIGS. 6A and 6B, the fixation element 61 and theendplate 62 have a different mating interface from that depicted inFIGS. 5A and 5B. As shown in FIGS. 6A and 6B, the gear teeth in theendplate are brought in contact with the corresponding gear teeth of theclamping element 63 that is attached to the fixation element 61 througha spring 64. In this mechanism, the slots next to the gear teeth shownin the embodiment depicted in FIGS. 5A and 5B are replaced by a springattached to the fixation element and this spring deformation providesthe necessary recess of the clamping element as the disc endplate ispushed in upon implantation. The gear teeth contact between the endplateand the clamping element allows one way sliding. The disc endplates andthe fixation elements have the rail interface as in FIGS. 5A and 5B toprevent the vertical movement.

II. Systems

Also provided are systems that include at least one component of thesubject prosthetic discs, as described above. The systems of the subjectinvention typically include all of the elements that may be necessaryand/or desired in order to replace an intervertebral disc with aprosthetic disc as described above. As such, at a minimum the subjectsystems include a prosthetic disc according to the present invention, asdescribed above. In addition, the systems in certain embodiments includea vertebral body fixation element, or components thereof, e.g., thefixation elements shown in FIGS. 5A to 6B, bone screws for securingintegrated fixation elements as shown in FIGS. 4A and 4B, and the like.The subject systems may also include special delivery devices, e.g., asdescribed in greater detail below.

One specific representative system of particular interest is depicted inFIG. 7. The system 70 of FIG. 7 is depicted as an exploded view, andincludes upper and lower fixation elements 71A and 71B, and disc 74 madeup of top and bottom endplates 72A and 72B, as well as the fibrouscompressible element 75, made up of both a fibrous component 73 andpolymeric component 76 of the prosthetic disc.

III. Methods of Use

Also provided are methods of using the subject prosthetic intervertebraldiscs and systems thereof. The subject prosthetic intervertebral discsand systems thereof find use in the replacement of damaged ordysfunctional interverterbral discs in vertebrate organisms. Generallythe vertebrate organisms are “mammals” or “mammalian,” where these termsare used broadly to describe organisms which are within the classmammalia, including the orders carnivore (e.g., dogs and cats), rodentia(e.g., mice, guinea pigs, and rats), lagomorpha (e.g. rabbits) andprimates (e.g., humans, chimpanzees, and monkeys). In many embodiments,the subjects will be humans.

In general, the devices are employed by first removing the to bereplaced disc from the subject or patient according to standardprotocols to produce a disc void space. Next, the subject prostheticdisc is implanted or positioned in the disc void space, resulting inreplacement of the removed disc with the prosthetic disc. Thisimplantation step may include a vertebral body fixation elementimplantation substep, a post implantation vertebral body securing step,or other variations, depending on the particular configuration of theprosthetic device being employed. In addition, the implantation stepdescribed above may include use of one or more implantation devices (ordisc delivery devices) for implanting the system components to the siteof implantation.

A representative implantation protocol for implanting the devicedepicted in FIG. 7 is now provided. First, the spine of a subject isexposed via a retroperitoneal approach after sterile preparation. Theintervertebral disc in trauma condition is removed, and the cartilageendplates above and below the disc are also removed to the bony endplates to obtain the bleeding surface for the bone growth into porouscavities in the spiked fixation elements 71A and 72A. The gap resultingfrom these removals is measured and the proper artificial disk assemblyis chosen according to the measurement.

The spiked fixation element plates are loaded onto a delivery instrument80 as shown in FIGS. 8 and 9 such that relative location and orientationbetween the upper spiked fixation element plate and the lower spikedfixation element plate are kept at a desired configuration. Thisconfiguration can be realized by providing appropriate mating featureson the instrument and the corresponding mating features on the spikedplates. One of the possible mating features would be the pocket of theinstrument and the corresponding external faces of the spiked plates asshown in FIG. 8. The pocket has the same internal face as the externalface of spiked plates but with a slightly smaller size such that thespiked plate fits tightly into the pocket of the instrument. Theinstrument together with the spiked fixation plates is delivered to thearea where the disc was removed and the spiked plates are pushed againstthe vertebra using the distracting motion of the instrument as shown inFIG. 9.

Once the spiked fixation plates are firmly fixed to the vertebra, theprosthetic disc 75 is held by a different tool and inserted into theimplanted spiked fixation plates such that its gear teeth go through thematching gear teeth on the spiked fixation plates. FIG. 10 shows thetool holding the disc. The grippers in FIG. 10 hold the fiber area ofthe disc when it is in grasp position. The disc accommodating thegrippers has the circular concave area in contact with the disc and ispushed into the spiked fixation plates through this contact. When thedisc is inserted all the way into the spiked plates, the protruded railson the disc at its most front side are in contact with the femalerailway of the spiked fixation plates and the disc is secured betweenthe spiked fixation plates and therefore the vertebra.

The above-described protocol is depicted in FIG. 11.

The above specifically reviewed protocol is merely representative of theprotocols that may be employed for implanting devices according to thesubject invention.

IV. Kits

Also provided are kits for use in practicing the subject methods, wherethe kits typically include one or more of the above prostheticintervertebral disc devices (e.g., a plurality of such devices indifferent sizes), and/or components of the subject systems, e.g.,fixation elements or components thereof, delivery devices, etc. asdescribed above. The kit may further include other components, e.g.,site preparation components, etc., which may find use in practicing thesubject methods.

In addition to above-mentioned components, the subject kits typicallyfurther include instructions for using the components of the kit topractice the subject methods. The instructions for practicing thesubject methods are generally recorded on a suitable recording medium.For example, the instructions may be printed on a substrate, such aspaper or plastic, etc. As such, the instructions may be present in thekits as a package insert, in the labeling of the container of the kit orcomponents thereof (i.e., associated with the packaging orsub-packaging) etc. In other embodiments, the instructions are presentas an electronic storage data file present on a suitable computerreadable storage medium, e.g. CD-ROM, diskette, etc. In yet otherembodiments, the actual instructions are not present in the kit, butmeans for obtaining the instructions from a remote source, e.g. via theinternet, are provided. An example of this embodiment is a kit thatincludes a web address where the instructions can be viewed and/or fromwhich the instructions can be downloaded. As with the instructions, thismeans for obtaining the instructions is recorded on a suitablesubstrate.

It is evident from the above discussion and results that the subjectinvention provides a significantly improved prosthetic intervertebraldisc. Significantly, the subject discs closely imitate the mechanicalproperties of the fully functional natural discs that they are designedto replace. The subject discs exhibit stiffness in the verticaldirection, torsional stiffness, bending stiffness in saggital plane, andbending stiffness in front plane, where the degree of these features canbe controlled independently by adjusting the components of the discs,e.g., number of layers of fiber winding, pattern of fiber winding,distribution of impregnated polymer, and the types of impregnatedpolymers, etc. The fiber reinforced structure of the subject discsprevents the fatigue failure on the inside polymer and the surfacetreatment on the fiber of certain embodiments eliminates the debrisproblem, both of which are major disadvantages experienced with certain“rubber-type” artificial disks. The interface mechanism between thefixation plates and the disc plates of certain embodiments of thesubject invention, e.g., as shown in FIG. 7, enables a very easysurgical operation. The surgeon simply needs to push the disc inwardafter fixing the spiked fixation plates onto the vertebrae. Suchembodiments also enable easy removal of the disc in case the surgerybrings about an ill effect. The gear teeth on the fixation elements areeasily pushed from outside such that the gear engagement between thedisc endplates and the fixation elements is released and the discendplates are pulled out from the spiked plates. In view of the aboveand other benefits and features provided by the subject invention, it isclear that the subject invention represents a significant contributionto the art.

Part B

With reference to the embodiments illustrated in FIGS. 12-54, thesubject prosthetic discs include upper and lower endplates separated bya core member. In one embodiment, the prosthetic disc comprises anintegrated, single-piece structure. In another embodiment, theprosthetic disc comprises a two-piece structure including a lowerendplate, and an upper endplate and the core member. The core may beassembled or integrated with either or the two endplates. The two-piecestructure may be a constrained structure, wherein the upper endplateassembly is attached to the lower endplate in a manner that preventsrelative rotation. Alternatively, the structure may be asemi-constrained or an unconstrained structure, wherein the upperendplate assembly is attached to the lower endplate in a manner thatallows relative rotation. In yet another embodiment, the prosthetic disccomprises a three-piece structure including upper and lower endplatesand a separable core member that is captured between the upper and lowerendplates by a retaining mechanism. Finally, in yet another embodiment,the prosthetic disc comprises a four-piece structure including upper andlower endplates and two separable core assemblies which, together, forma core member. Those of ordinary skill in the art will recognize thatfive-piece, six-piece, or other multi-piece structures may beconstructed by further division of the core member and/or the upper andlower endplates, or by the provision of additional components to thestructure.

The implantation apparatus and methods are adapted to implant theprosthetic discs between two adjacent vertebral bodies of a patient. Ina first embodiment, the apparatus includes three implantation tools usedto prepare the two adjacent vertebral bodies for implantation and thento implant the prosthetic disc. A first tool, a spacer, is adapted to beinserted between and to separate the two adjacent vertebral bodies tocreate sufficient space for implanting the prosthetic disc. A secondtool, a chisel, includes one or more wedge-shaped cutting blades locatedon its upper and/or lower surfaces that are adapted to create grooves inthe inward facing surfaces of the two adjacent vertebral bodies. A thirdtool, a holder, includes an engagement mechanism adapted to hold theprosthetic disc in place while it is being implanted, and to release thedisc once it has been implanted.

In another embodiment, the implantation apparatus includes a guidemember that engages the lower endplate and that remains in place duringa portion of the disc implantation process. A lower pusher memberslidably engages the guide member and is used to advance the lowerendplate into place between two adjacent vertebral bodies of a patient'sspine. An upper pusher member is preferably coupled to the lower pushermember and is used to advance a first chisel into place opposed to thelower endplate between the two adjacent vertebral bodies. Once in place,an upward force is applied to the upper pusher member to cause the firstchisel to engage the upper vertebral body and to chisel one or moregrooves into its lower surface. A downward force is also applied to thelower pusher member to cause the lower endplate to engage the lowervertebral body and to become implanted. The upper pusher member andfirst chisel are then removed, as is the lower pusher member.Preferably, a second chisel is then advanced along the guide member andis used to provide additional preparation of the upper vertebral body.After the completion of the preparation by the first chisel and,preferably, the second chisel, the upper endplate and core members ofthe prosthetic disc are implanted using an upper endplate holder that isadvanced along the guide member. After implantation, the upper endplateholder and guide member are removed.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentinventions.

I. Prosthetic Intervertebral Discs

The prosthetic intervertebral discs are preferably artificial or manmadedevices that are configured or shaped so that they can be employed asreplacements for an intervertebral disc in the spine of a vertebrateorganism, e.g., a mammal, such as a human. The subject prostheticintervertebral discs have dimensions that permit them to substantiallyoccupy the space between two adjacent vertebral bodies that is presentwhen the naturally occurring disc between the two adjacent bodies isremoved, i.e., a disc void space. By substantially occupy is meant thatthe prosthetic disc occupies a sufficient volume in the space betweentwo adjacent vertebral bodies that the disc is able to perform some orall of the functions performed by the natural disc for which it servesas a replacement. In certain embodiments, subject prosthetic discs mayhave a roughly bean shaped structure analogous to naturally occurringintervertebral body discs. In many embodiments, the length of theprosthetic discs range from about 15 mm to about 50 mm, preferably fromabout 18 mm to about 46 mm, the width of the prosthetic discs range fromabout 12 mm to about 30 mm, preferably from about 14 mm to about 25 mm,and the height of the prosthetic discs range from about 3 mm to about 15mm, preferably from about 5 mm to about 14 mm.

The prosthetic discs include upper and lower endplates separated by acore member. The resulting structure provides a prosthetic disc thatfunctionally closely mimics a natural disc.

A. One-Piece Structure

Representative prosthetic intervertebral discs 100 having one-piecestructures are shown in FIGS. 12 through 15. The prosthetic discincludes an upper endplate 110, a lower endplate 120, and a core member130 retained between the upper endplate 110 and the lower endplate 120.One or more fibers 140 are wound around the upper and lower endplates toattach the endplates to one another. (For clarity, the fibers 140 arenot shown in all of the Figures. Nevertheless, fibers 140, as shown, forexample, in FIG. 12, are present in and perform similar functions ineach of the embodiments described herein.) The fibers 140 preferably arenot tightly wound, thereby allowing a degree of axial rotation, bending,flexion, and extension by and between the endplates. The core member 130may be provided in an uncompressed or a pre-compressed state. An annularcapsule 150 is optionally provided in the space between the upper andlower endplates, surrounding the core member 130 and the fibers 140. Theupper endplate 110 and lower endplate 120 are generally flat, planarmembers, and are fabricated from a physiologically acceptable materialthat provides substantial rigidity. Examples of materials suitable foruse in fabricating the upper endplate 110 and lower endplate 120 includetitanium, titanium alloys, stainless steel, cobalt/chromium, etc., whichare manufactured by machining or metal injection molding; plastics suchas polyethylene with ultra high molar mass (molecular weight) (UHMWPE),polyether ether ketone (PEEK), etc., which are manufactured by injectionmolding or compression molding; ceramics; graphite; and others.Optionally, the endplates may be coated with hydroxyapatite, titaniumplasma spray, or other coatings to enhance bony ingrowth.

As noted above, the upper and lower endplates typically have a length offrom about 12 mm to about 45 mm, preferably from about 13 mm to about 44mm, a width of from about 11 mm to about 28 mm, preferably from about 12mm to about 25 mm, and a thickness of from about 0.5 mm to about 4 mm,preferably from about 1 mm to about 3 mm. The sizes of the upper andlower endplates are selected primarily based upon the size of the voidbetween adjacent vertebral bodies to be occupied by the prosthetic disc.Accordingly, while endplate lengths and widths outside of the rangeslisted above are possible, they are not typical.

The upper surface of the upper endplate 110 and the lower surface of thelower endplate 120 are preferably each provided with a mechanism forsecuring the endplate to the respective opposed surfaces of the upperand lower vertebral bodies between which the prosthetic disc is to beinstalled. For example, in FIG. 12, the upper endplate 110 includes aplurality of anchoring fins 111 a-b. The anchoring fins 111 a-b areintended to engage mating grooves that are formed on the surfaces of theupper and lower vertebral bodies to thereby secure the endplate to itsrespective vertebral body. The anchoring fins 111 a-b extend generallyperpendicularly from the generally planar external surface of the upperendplate 110, i.e., upward from the upper side of the endplate as shownin FIG. 12. In the FIG. 12 embodiment, the upper endplate 110 includesthree anchoring fins 111 a-c, although only two are shown in thecross-sectional view. A first of the anchoring fins, 111 a, is disposednear an external edge of the external surface of the upper endplate andhas a length that approximates the width of the upper endplate 110. Asecond of the anchoring fins, 111 b, is disposed at the center ofexternal surface of the upper endplate and has a relatively shorterlength, substantially less than the width of the upper endplate 110.Each of the anchoring fins 111 a-b has a plurality of serrations 112located on the top edge of the anchoring fin. The serrations 112 areintended to enhance the ability of the anchoring fin to engage thevertebral body and to thereby secure the upper endplate 110 to thespine.

Similarly, the lower surface of the lower endplate 120 includes aplurality of anchoring fins 121 a-b. The anchoring fins 121 a-b on thelower surface of the lower endplate 120 are identical in structure andfunction to the anchoring fins 111 a-b on the upper surface of the upperendplate 110, with the exception of their location on the prostheticdisc. The anchoring fins 121 a-b on the lower endplate 120 are intendedto engage mating grooves formed on the lower vertebral body, whereas theanchoring fins 111 a-b on the upper endplate 110 are intended to engagemating grooves on the upper vertebral body. Thus, the prosthetic disc100 is held in place between the adjacent vertebral bodies.

The anchoring fins 111, 121 may optionally be provided with one or moreholes or slots 115, 125. The holes or slots help to promote bonyingrowths that bond the prosthetic disc 100 to the vertebral bodies.

Turning to FIGS. 13A-C, there are shown several alternative mechanismsfor securing the endplates to the respective opposed surfaces of theupper and lower vertebral bodies between which the prosthetic disc is tobe installed. In FIG. 13A, each of the upper endplate 110 and lowerendplate 120 is provided with a single anchoring fin 111, 121. Theanchoring fins 111, 121 are located along a center line of therespective endplates, and each is provided with a plurality ofserrations 112, 122 on its upper edge. The single anchoring fins 111,121 are intended to engage grooves formed on the opposed surface of theupper and lower vertebral bodies, as described above. In FIG. 13B, eachof the upper endplate 110 and lower endplate 120 is provided with threeanchoring fins 111 a-c, 121 a-c. The FIG. 13B prosthetic disc is thesame as the prosthetic disc shown in FIG. 1, but it is shown inperspective rather than cross-section. Thus, the structure and functionof the anchoring fins 111 a-c and 121 a-c are as described above inrelation to FIG. 12. Finally, in FIG. 13C, each of the upper endplate110 and lower endplate 120 is provided with a plurality of serrations113, 123 over a portion of the exposed external surface of therespective endplate. The serrations 113, 123 are intended to engage theopposed surfaces of the adjacent vertebral bodies to thereby secure theendplates in place between the vertebral bodies. The serrations 113, 123may be provided over the entire external surface of each of the upperand lower endplates, or they may be provided over only a portion ofthose surfaces. For example, in FIG. 13C, the serrations 113 on theupper surface of the upper endplate 110 are provided over three majorareas, a first area 113 a near a first edge of the upper endplate 110, asecond area 113 b near the center of the upper endplate 110, and a thirdarea near a second edge of the endplate 113 c.

Turning to FIG. 54, in an optional embodiment, the anchoring fins 111are selectively retractable and extendable by providing a deploymentmechanism 160 that is associated with the upper endplate 110. A similarmechanism may be used on the lower endplate 120. The deploymentmechanism includes a slider 161 that slides within a channel 162 formedin the upper endplate 110. The channel 162 includes a threaded region163, and the slider 161 includes matching threads 164, thereby providinga mechanism for advancing the slider 161 within the channel 162. As theslider 161 is advanced within the channel 162, a tapered region 165engages the bottom surface of a deployable fin 166. Further advancementof the slider 161 causes the deployable fin 166 to be raised upwardwithin a slot 167 on the upper surface of the upper endplate 110.Reversing the deployment mechanism 160 causes the fin 166 to retract.The deployment mechanism 160 may also be used in conjunction withspikes, serrations, or other anchoring devices. In an alternativeembodiment, the threaded slider 161 of the deployment mechanism may bereplaced with a dowel pin that is advanced to deploy the fin 166. Otheradvancement mechanisms are also possible.

Returning to FIG. 12, the upper endplate 110 contains a plurality ofslots 114 through which the fibers 140 may be passed through or wound,as shown. The actual number of slots 114 contained on the endplate isvariable. Increasing the number of slots will result in an increase inthe circumferential density of the fibers holding the endplatestogether. In addition, the shape of the slots may be selected so as toprovide a variable width along the length of the slot. For example, thewidth of the slots may taper from a wider inner end to a narrow outerend, or visa versa. Additionally, the fibers may be wound multiple timeswithin the same slot, thereby increasing the radial density of thefibers. In each case, this improves the wear resistance and increasesthe torsional and flexural stiffness of the prosthetic disc, therebyfurther approximating natural disc stiffness. In addition, the fibers140 may be passed through or wound on each slot, or only on selectedslots, as needed. Two exemplary winding patterns are shown in FIGS. 14Aand 14B. In FIG. 14A, the fibers 140 are wound in a uni-directionalmanner, which closely mimics natural annular fibers found in a naturaldisc. In FIG. 14B, the fibers 140 are wound bi-directionally. Otherwinding patterns, either single or multi-directional, are also possible.

As described above, the purpose of the fibers 140 is to hold the upperendplate 110 and lower endplate 120 together and to limit therange-of-motion to mimic the range-of-motion of a natural disc.Accordingly, the fibers preferably comprise high tenacity fibers with ahigh modulus of elasticity, for example, at least about 100 MPa, andpreferably at least about 500 MPa. By high tenacity fibers is meantfibers that can withstand a longitudinal stress of at least 50 MPa, andpreferably at least 250 MPa, without tearing. The fibers 140 aregenerally elongate fibers having a diameter that ranges from about 100μm to about 500 μm, and preferably about 200 μm to about 400 μm.Optionally, the fibers may be injection molded with an elastomer toencapsulate the fibers, thereby providing protection from tissueingrowth and improving torsional and flexural stiffness, or the fibersmay be coated with one or more other materials to improve fiberstiffness and wear. Additionally, the core may be injected with awetting agent such as saline to wet the fibers and facilitate themimicking of the viscoelastic properties of a natural disc.

The fibers 140 may be fabricated from any suitable material. Examples ofsuitable materials include polyester (e.g., Dacron®), polyethylene,polyaramid, poly-paraphenylene terephthalamide (e.g., Kevlar®), carbonor glass fibers, polyethylene terephthalate, acrylic polymers,methacrylic polymers, polyurethane, polyurea, polyolefin, halogenatedpolyolefin, polysaccharide, vinylic polymer, polyphosphazene,polysiloxane, and the like.

The fibers 140 may be terminated on an endplate by tying a knot in thefiber on the superior surface of an endplate. Alternatively, the fibers140 may be terminated on an endplate by slipping the terminal end of thefiber into a slot on an edge of an endplate, similar to the manner inwhich thread is retained on a thread spool. The slot may hold the fiberwith a crimp of the slot structure itself, or by an additional retainersuch as a ferrule crimp. As a further alternative, tab-like crimps maybe machined into or welded onto the endplate structure to secure theterminal end of the fiber. The fiber may then be closed within the crimpto secure it. As a still further alternative, a polymer may be used tosecure the fiber to the endplate by welding. The polymer wouldpreferably be of the same material as the fiber (e.g., PE, PET, or theother materials listed above). Still further, the fiber may be retainedon the endplates by crimping a cross-member to the fiber creating aT-joint, or by crimping a ball to the fiber to create a ball joint.

The core member 130 is intended to provide support to and to maintainthe relative spacing between the upper endplate 110 and lower endplate120. The core member 130 is made of a relatively compliant material, forexample, polyurethane or silicone, and is typically fabricated byinjection molding. A preferred construction for the core member includesa nucleus formed of a hydrogel and an elastomer reinforced fiberannulus. For example, the nucleus, the central portion of the coremember 130, may comprise a hydrogel material such as a water absorbingpolyurethane, polyvinyl alcohol (PVA), polyethylene oxide (PEO),polyvinylpyrrolidone (PVP), polyacrylamide, silicone, or PEO basedpolyurethane. The annulus may comprise an elastomer, such as silicone,polyurethane or polyester (e.g., Hytrel®), reinforced with a fiber, suchas polyethylene (e.g., ultra high molecular weight polyethylene,UHMWPE), polyethylene terephthalate, or poly-paraphenyleneterephthalamide (e.g., Kevlar®).

The shape of the core member 130 is typically generally cylindrical orbean-shaped, although the shape (as well as the materials making up thecore member and the core member size) may be varied to obtain desiredphysical or performance properties. For example, the core member 130shape, size, and materials will directly affect the degree of flexion,extension, lateral bending, and axial rotation of the prosthetic disc.

The annular capsule 150 is preferably made of polyurethane or siliconeand may be fabricated by injection molding, two-part component mixing,or dipping the endplate-core-fiber assembly into a polymer solution. Apreferred annular capsule 150 is shown in FIGS. 15A-C. As shown, theannular capsule is generally cylindrical, having an upper circular edge153, a lower circular edge 154, and a generally cylindrical body 155. Inthe embodiment shown in the Figures, the body 155 has two bellows 156a-b formed therein. Alternative embodiments have no bellows, one bellow,or three or more bellows. A function of the annular capsule is to act asa barrier that keeps the disc materials (e.g., fiber strands) within thebody of the disc, and that keeps natural in-growth outside the disc.

Additional examples of the one-piece structure embodiment of theprosthetic disc are illustrated in FIGS. 13D-F. Each of theseembodiments includes an upper endplate 110, lower endplate 120, and acore member 130, as described above. The upper endplate 110 includes anouter portion 110 a and an inner portion 110 b, and the lower endplatealso includes an outer portion 120 a and an inner portion 120 b. Theinner and outer portions of each of the endplates are bonded to eachother by methods known to those of skill in the art. Each of theendplates 110, 120 also includes anchoring fins 111 a-c, 121 a-c on theupper surface of the upper endplate 110 and the lower surface of thelower endplate 120, as also described above. Additionally, withreference to FIG. 13D, a superior dome 116 is provided on the uppersurface of the upper endplate 110. The superior dome 116 is a generallyconvex portion that extends upward from the upper surface of the upperendplate 110. The superior dome 116 is optional, and functions byfilling space between the upper endplate 110 and the vertebral body uponimplantation to help approximate the upper endplate 110 to the naturalanatomy. The size and shape of the superior dome 116 may be variedaccording to need. As shown in FIG. 13D, the superior dome 116 isgenerally convex and has a maximum height (distance above the generallyflat upper surface portion of the upper endplate) of approximatelyone-half the height of the anchoring fin 111 b. The superior dome 116may be centered in the middle of the upper endplate 110, as shown inFIG. 2D, or it may be shifted to one side or another, depending on need.

With particular reference to FIG. 13F, a polymer film 170 is sandwichedbetween the outer portion 10 a and inner portion 10 b of the upperendplate 110, and another polymer film 170 is sandwiched between theouter portion 120 a and inner portion 120 b of the lower endplate 120.The polymer films 170 are adapted to tightly adhere, either mechanicallyor chemically, to the fibers 140 wound through the slots 114, 124 formedin the upper endplate 110 and lower endplate 120.

FIGS. 13D-F provide additional detail concerning the annular capsule150. As shown there, the annular capsule 150 seals the interior spacebetween the upper and lower endplates. The annular capsule 150 isretained on the disc by a pair of retaining rings 151 that engage amating pair of external facing grooves 152 on the upper and lowerendplates. (See FIG. 13F). Although the retaining rings may be of anysuitable cross-section (e.g., round, triangular, square, etc.), theexamples shown in FIG. 13F have a rectangular cross-section. Therectangular shape is believed to provide relatively better gasketretention and is more easily manufactured.

FIGS. 13G and 13H illustrate still further examples of the one-piecestructure embodiment of the prosthetic disc. In the examples shownthere, the upper endplate 110 includes an outer portion 110 a and aninner portion 110 b. Similarly, the lower endplate 120 includes an outerportion 120 a and an inner portion 120 b. The two portions 110 a-b, 120a-b of each of the upper and lower endplates mate together to form theintegrated upper endplate 110 and lower endplate 120. Preferably, thetwo portions 110 a-b, 120 a-b of the upper and lower endplates 110, 120are joined together by welding, e.g., laser welding or some similarprocess. An advantage that may be obtained with this structure is theability to retain the annular capsule 150 (not shown in FIGS. 13G-H)without the need for a separate retaining ring. For example, the upperedge of the annular capsule may be captured and retained between theouter portion 110 a and inner portion 110 b of the upper endplate 110when they are attached to one another. Similarly, the lower edge of theannular capsule may be captured and retained between the outer portion120 a and inner portion 120 b of the lower endplate 120 when thosecomponents are attached to one another. In this manner, the annularcapsule is held in place between the upper and lower endplates by thecompression forces retaining the upper and lower edges of the annularcapsule.

An optional structure for retaining the annular capsule 150 isillustrated in FIGS. 13I-J. There, an upper endplate 110 is shownincluding an outer portion 110 a and an inner portion 110 b. The uppersurface of the inner portion 110 b of the upper endplate 110 is providedwith an annular groove 117 that extends about the periphery of the innerportion 110 b. The annular groove 117 cooperates with the bottom surfaceof the outer portion 110 a of the upper endplate 110 to create anannular space 118. A similar structure, not shown in the drawings, maybe provided on the lower endplate 120. The annular capsule 150 (notshown in FIGS. 13I-J) may advantageously be formed having a bead, i.e.,a ball-like termination about its upper and lower edge, (also not shownin the drawings), that occupies the annular space 118 formed on theupper and lower endplates 110, 120. The cooperation of the annular space118 with the bead formed on the annular capsule 150 creates a strongerand more secure retaining force for retaining the upper and lower edgeof the annular capsule 150 by the upper and lower endplates 1110, 120.Alternatively, the annular capsule may be retained by adhesives with orwithout the endplate compression already described.

Another optional feature of the present invention is the placement ofthe fibers in a state of tensile fatigue upon fabrication so as tominimize long-term wear. For example, in the embodiment of FIGS. 13I-J,a material 131 such as a metal plate or a polymer film may be positionedwithin space 119 of upper portion 1110 a of the endplate and between thefibers 127 and the surface of the endplate. The material may initiallybe in a form, e.g., gel or emulsion, so as to coat and impregnate thefibers. With such material, the fibers are caused to impinge upon theendplate thereby reducing their susceptibility to movement during use ofthe disc. As an additional optional feature, each of the endplates maybe made up of two plates that are selectively rotationally displaceablerelative to each other. In this structure, a slight rotation of one ofthe plates relative to the other has the effect of changing the sizeand/or shape of the slots formed on the combined endplate. Thus, theuser is able to select a desired set of dimensions of the slots.

FIGS. 13K-L illustrate another optional feature that may be incorporatedin the one-piece structure embodiment of the prosthetic disc. In theexamples shown there, a spring 180 is located coaxially with the coremember 130 between the upper endplate 10 and lower endplate 120. In thisexample, the core member 130 is in the form of a toroid, thus having aspace at its center. The spring 180 is placed in the space at the centerof the core member 130, with each being retained between the upperendplate 110 and lower endplate 120. The spring 180 provides a forcebiasing the two endplates apart, and having performance characteristicsand properties that are different from those provided by the core member130. Those characteristics may be varied by, for example, selecting aspring 180 having different dimensions, materials, or a different springconstant. In this way, the spring 180 provides an additional mechanismby which the performance of the prosthetic disc may be varied in orderto approximate that of a natural disc.

Turning to FIGS. 50A-B, additional examples of the one-piece structureembodiment of the prosthetic discs are shown. The discs illustrated inFIGS. 50A-B are particularly adapted in size and shape for implantationby minimally invasive surgical procedures, as described below. Asidefrom their size and shape, the structures of the examples shown in FIGS.50A-B are similar to those described above, including an upper endplate110, lower endplate 120, a core member 130, and an annular capsule 150.Each of the upper and lower endplates 110, 120 is provided with ananchoring fin 111, 121 extending from its surface over most of thelength of the endplate. Although not shown in the drawings, theseexamples also preferably include fibers 140 wound between and connectingthe upper endplate 110 to the lower endplate 120.

In the example shown in FIG. 50A, a single elongated core member isprovided, whereas the example structure shown in FIG. 50B has a dualcore including two generally cylindrical core members 130 a, 130 b. Itis believed that the dual core structure (FIG. 50B) better simulates theperformance characteristics of a natural disc. In addition, the dualcore structure is believed to provide less stress on the fibers 140relative to the single core structure (FIG. 50A). Each of the exemplaryprosthetic discs shown in FIGS. 50A-B has a greater length than width.Exemplary shapes to provide these relative dimensions includerectangular, oval, bullet-shaped, or others. This shape facilitatesimplantation of the discs by the minimally invasive procedures describedbelow.

The one-piece structure embodiment of the prosthetic disc is implantedby a surgical procedure. After removing the natural disc, grooves areformed in the superior and inferior vertebrae between which theprosthetic disc is to be implanted. The prosthetic disc is then insertedinto the void, while aligning the anchoring fins 111, 121 with thegrooves formed on the vertebral bodies. The anchoring fins cause theprosthetic disc to be secured in place between the adjacent vertebralbodies. The prosthetic disc has several advantages over prior artartificial discs, as well as over alternative treatment procedures suchas spinal fusion. For example, the prosthetic discs described hereinprovide compressive compliance similar to that of a natural spinal disc.In addition, the motions in flexion, extension, lateral bending, andaxial rotation are also restricted in a manner near or identical tothose associated with a natural disc.

B. Two-Piece Structure

Representative prosthetic intervertebral discs 200 having two-piecestructures are shown in FIGS. 16 through 20. The components and featuresincluded in the two-piece prosthetic discs are very similar to those ofthe one-piece disc described above. A primary difference between thedevices is that the two-piece prosthetic disc contains two separablecomponents, whereas the one-piece prosthetic disc contains a single,integrated structure. In particular, and as described more fully below,the lower endplate of the two-piece prosthetic disc is separated into aninner lower endplate 220 a, and an outer lower endplate 220 b (see FIGS.16-20), whereas there is only a single lower endplate 120 in theone-piece disc (see FIGS. 12 and 13A-C).

Turning to FIGS. 16-20, the two-piece prosthetic disc includes twoprimary, separable components: the outer lower endplate 220 b, and anupper subassembly 205. In a first embodiment of the two-piece prostheticdisc, shown in FIGS. 16-18, the upper subassembly 205 is constrained,i.e., it cannot freely rotate in relation to the outer lower endplate220 b. In a second embodiment of the two-piece prosthetic disc, shown inFIGS. 19-20, the upper subassembly 205 is unconstrained, i.e., it cansubstantially freely rotate in relation to the outer lower endplate 220b.

The upper subassembly includes the inner lower endplate 220 a, an upperendplate 210, and a core member 230 retained between the upper endplate210 and the inner lower endplate 220 a. One or more fibers 240 are woundaround the upper and inner lower endplates to attach the endplates toone another. The fibers 240 preferably are not tightly wound, therebyallowing a degree of axial rotation, bending, flexion, and extension byand between the endplates. The core member 230 is preferablypre-compressed. An annular capsule 250 is optionally provided in thespace between the upper and inner lower endplates, surrounding the coremember 230 and the fibers 240. Alternatively, an outer ring or gasket(not shown in the drawings) may optionally be provided in place of theannular capsule 250.

The upper endplate 210 and outer lower endplate 220 b are generallyflat, planar members, and are fabricated from a physiologicallyacceptable material that provides substantial rigidity. Examples ofmaterials suitable for use in fabricating the upper endplate 210 andouter lower endplate 220 b include titanium, titanium alloys, stainlesssteel, cobalt/chromium, etc., which are manufactured by machining ormetal injection molding; plastics such as polyethylene with ultra highmolar mass (molecular weight) (UHMWPE), polyether ether ketone (PEEK),etc., which are manufactured by injection molding or compressionmolding; ceramics; graphite; and others. Optionally, the endplates maybe coated with hydroxyapatite, titanium plasma spray, or other coatingsto enhance bony ingrowth.

As noted above, the upper and outer lower endplates typically have alength of from about 12 mm to about 45 mm, preferably from about 13 mmto about 44 mm, a width of from about 11 mm to about 28 mm, preferablyfrom about 12 mm to about 25 mm, and a thickness of from about 0.5 mm toabout 4 mm, preferably from about 1 mm to about 3 mm. The sizes of theupper and outer lower endplates are selected primarily based upon thesize of the void between adjacent vertebral bodies to be occupied by theprosthetic disc. Accordingly, while endplate lengths and widths outsideof the ranges listed above are possible, they are not typical.

The upper surface of the upper endplate 210 and the lower surface of theouter lower endplate 220 b are preferably each provided with a mechanismfor securing the endplate to the respective opposed surfaces of theupper and lower vertebral bodies between which the prosthetic disc is tobe implanted. For example, as shown in FIGS. 16 and 18-20, the upperendplate 210 includes a plurality of anchoring fins 211 a-c. Theanchoring fins 211 a-c are intended to engage mating grooves that areformed on the surfaces of the upper and lower vertebral bodies tothereby secure the endplate to its respective vertebral body. Theanchoring fins 211 a-c extend generally perpendicular from the generallyplanar external surface of the upper endplate 210, i.e., upward from theupper side of the endplate as shown in FIG. 16. In the FIG. 16embodiment, the upper endplate 210 includes three anchoring fins 211a-c. The first and third of the anchoring fins, 211 a and 211 c, aredisposed near the external edges of the external surface of the upperendplate 210 and have lengths that approximate the width of the upperendplate 210. The second of the anchoring fins, 211 b, is disposed atthe center of external surface of the upper endplate and has arelatively shorter length, substantially less than the width of theupper endplate 210. Each of the anchoring fins 211 a-c has a pluralityof serrations 212 located on the top edge of the anchoring fin. Theserrations 212 are intended to enhance the ability of the anchoring finto engage the vertebral body and to thereby secure the upper endplate210 to the vertebral body.

The lower surface of the outer lower endplate 220 b includes a pluralityof anchoring spikes 221. The anchoring spikes 221 on the lower surfaceof the outer lower endplate 220 b are intended to engage the surface ofthe lower vertebral body, while the anchoring fins 211 a-c on the upperendplate 210 are intended to engage mating grooves on the uppervertebral body. Thus, the prosthetic disc 200 is held in place betweenthe adjacent vertebral bodies.

Alternatively, the upper endplate 210 and outer lower endplate 220 b ofthe two-piece prosthetic disc may employ one of the alternative securingmechanisms shown in FIGS. 13A-C. As described above, in FIG. 13A, eachof the upper endplate 110 and lower endplate 120 is provided with asingle anchoring fin 111, 121. The anchoring fins 111, 121 are locatedalong a center line of the respective endplates, and each is providedwith a plurality of serrations 112, 122 on its upper edge. The singleanchoring fins 111, 121 are intended to engage grooves formed on theopposed surface of the upper and lower vertebral bodies, as describedabove. In FIG. 13B, each of the upper endplate 110 and lower endplate120 is provided with three anchoring fins 111 a-c, 121 a-c. The FIG. 13Bprosthetic disc is the same as the prosthetic disc shown in FIG. 12, butit is shown in perspective rather than cross-section. Thus, thestructure and function of the anchoring fins 111 a-c and 121 a-c are asdescribed above in relation to FIG. 12. Finally, in FIG. 13C, each ofthe upper endplate 110 and lower endplate 120 is provided with aplurality of serrations 113, 123 over a portion of the exposed externalsurface of the respective endplate. The serrations 113, 123 are intendedto engage the opposed surfaces of the adjacent vertebral bodies tothereby secure the endplates in place between the vertebral bodies. Theserrations 113, 123 may be provided over the entire external surface ofeach of the upper and lower endplates, or they may be provided over onlya portion of those surfaces. For example, in FIG. 13C, the serrations113 on the upper surface of the upper endplate 110 are provided overthree major areas, a first area 113 a near a first edge of the upperendplate 110, a second area 113 b near the center of the upper endplate110, and a third area near a second edge of the endplate 113 c.

Turning to FIG. 54, in an optional embodiment, the anchoring fins 111are selectively retractable and extendable by providing a deploymentmechanism 160 that is associated with the upper endplate 110. A similarmechanism may be used on the lower endplate 120. The deploymentmechanism includes a slider 161 that slides within a channel 162 formedin the upper endplate 110. The channel 162 includes a threaded region163, and the slider 161 includes matching threads 164, thereby providinga mechanism for advancing the slider 161 within the channel 162. As theslider 161 is advanced within the channel 162, a tapered region 165engages the bottom surface of a deployable fin 166. Further advancementof the slider 161 causes the deployable fin 166 to be raised upwardwithin a slot 167 on the upper surface of the upper endplate 110.Reversing the deployment mechanism 160 causes the fin 166 to retract.The deployment mechanism 160 may also be used in conjunction withspikes, serrations, or other anchoring devices. In an alternativeembodiment, the threaded slider 161 of the deployment mechanism may bereplaced with a dowel pin that is advanced to deploy the fin 166. Otheradvancement mechanisms are also possible.

Returning to FIG. 18, the upper endplate 210 contains a plurality ofslots 214 through which the fibers 240 may be passed through or wound,as shown. The actual number of slots 214 contained on the endplate isvariable. Increasing the number of slots will result in an increase inthe circumferential density of the fibers holding the endplatestogether. Additionally, the fibers may be wound multiple times withinthe same slot, thereby increasing the radial density of the fibers. Ineach case, this improves the wear resistance and increases the torsionaland flexural stiffness of the prosthetic disc, thereby furtherapproximating natural disc stiffness. In addition, the fibers 240 may bepassed through or wound on each slot, or only on selected slots, asneeded.

As described above, the purpose of the fibers 240 is to hold the upperendplate 210 and lower endplate 220 together and to limit therange-of-motion to mimic the range-of-motion of a natural disc.Accordingly, the fibers preferably comprise high tenacity fibers with ahigh modulus of elasticity, for example, at least about 100 MPa, andpreferably at least about 500 MPa. By high tenacity fibers is meantfibers that can withstand a longitudinal stress of at least 50 MPa, andpreferably at least 250 MPa, without tearing. The fibers 240 aregenerally elongate fibers having a diameter that ranges from about 100μm to about 500 μm, and preferably about 200 μm to about 400 μm.Optionally, the fibers may be injection molded with an elastomer toencapsulate the fibers, thereby providing protection from tissueingrowth and improving torsional and flexural stiffness.

The fibers 240 may be fabricated from any suitable material. Examples ofsuitable materials include polyester (e.g., Dacron®), polyethylene,polyaramid, poly-paraphenylene terephthalamide (e.g., Kevlar®), carbonor glass fibers, polyethylene terephthalate, acrylic polymers,methacrylic polymers, polyurethane, polyurea, polyolefin, halogenatedpolyolefin, polysaccharide, vinylic polymer, polyphosphazene,polysiloxane, and the like.

The fibers 240 may be terminated on an endplate by tying a knot in thefiber on the superior surface of an endplate. Alternatively, the fibers240 may be terminated on an endplate by slipping the terminal end of thefiber into a slot on an edge of an endplate, similar to the manner inwhich thread is retained on a thread spool. The slot may hold the fiberwith a crimp of the slot structure itself, or by an additional retainersuch as a ferrule crimp. As a further alternative, tab-like crimps maybe machined into or welded onto the endplate structure to secure theterminal end of the fiber. The fiber may then be closed within the crimpto secure it. As a still further alternative, a polymer may be used tosecure the fiber to the endplate by welding. The polymer wouldpreferably be of the same material as the fiber (e.g., PE, PET, or theother materials listed above). Still further, the fiber may be retainedon the endplates by crimping a cross-member to the fiber creating aT-joint, or by crimping a ball to the fiber to create a ball joint.

The core member 230 is intended to provide support to and to maintainthe relative spacing between the upper endplate 210 and inner lowerendplate 220 a. The core member 230 is made of a relatively compliantmaterial, for example, polyurethane or silicone, and is typicallyfabricated by injection molding. A preferred construction for the coremember 230 includes a nucleus formed of a hydrogel and an elastomerreinforced fiber annulus. For example, the nucleus, the central portionof the core member 230, may comprise a hydrogel material such astecophilic water absorbing polyurethane, polyvinyl alcohol (PVA),polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polyacrylamide,silicone, or PEO based polyurethane. The annulus may comprise anelastomer, such as silicone, polyurethane or polyester (e.g., Hytrel®),reinforced with a fiber, such as polyethylene, polyethyleneterephthalate, or poly-paraphenylene terephthalamide (e.g., Kevlar®).

The shape of the core member 230 is typically generally cylindrical orbean-shaped, although the shape (as well as the materials making up thecore member and the core member size) may be varied to obtain desiredphysical or performance properties. For example, the core member 230shape, size, and materials will directly affect the degree of flexion,extension, lateral bending, and axial rotation of the prosthetic disc.

The annular capsule 250 is preferably made of polyurethane or siliconeand may be fabricated by injection molding, two-part component mixing,or dipping the endplate-core-fiber assembly into a polymer solution.Alternatively, an outer ring or gasket (not shown in the drawings) mayoptionally be provided in place of the annular capsule 250.

The upper subassembly 205 is configured to be selectively attached tothe outer lower endplate 220 b. As shown, for example, in FIGS. 3 and 6,the edges 225 of the inner lower endplate 220 a have a size and shapeadapted to engage slots 226 formed on the upper surface of the outerlower endplate 220 b. Accordingly, the upper subassembly 205 will slideonto the outer lower endplate 220 b, with the inner lower endplate edges225 engaging the outer lower endplate slots 226.

At this point, the differences between the constrained, semi-constrainedand unconstrained embodiments of the two-piece prosthetic disc will bedescribed. Turning first to the constrained embodiment shown in FIGS.16-18, once the upper subassembly 205 is fully advanced onto the outerlower endplate 220 b—i.e., once the leading edge 225 of the inner lowerendplate 220 a engages the back portion of the slot 226 of the outerlower endplate 220 b—a tab 261 on the bottom surface of the inner lowerendplate 220 a engages a notch 262 on the top surface of the outer lowerendplate 220 b (see FIG. 18), thereby locking the upper subassembly 205to the outer lower endplate 220 b. The tab 261 and notch 262 are squaredsurfaces, thereby preventing relative rotation between the inner lowerendplate 220 a and outer lower endplate 220 b. Additionally, the edges225 of the inner lower endplate 220 a and the mating slots 226 of theouter lower endplate 220 b include mating straight portions 227 and 228,respectively, which also tend to inhibit rotation of the inner lowerendplate 220 a relative to the outer lower endplate 220 b.

Turning next to the unconstrained embodiment shown in FIGS. 19-20, theouter lower endplate 220 b is provided with a raised lip 271. The raisedlip 271 is slightly downwardly displaceable, i.e., the raised lip 271will deflect downwardly when force is applied to it. Accordingly, whenthe upper subassembly is being attached to the outer lower endplate 220b, the raised lip will displace downwardly to allow the edges 225 of theinner lower endplate 220 a to engage the slots 226 of the outer lowerendplate 220 b. Once the upper subassembly 205 is fully advanced ontothe outer lower endplate 220 b—i.e., once the leading edge 225 of theinner lower endplate 220 a engages the back portion of the slot 226 ofthe outer lower endplate 220 b—the raised lip 271 snaps back into place,as shown in FIG. 20, thereby locking the upper subassembly 205 to theouter lower endplate 220 b. Notably, the raised lip 271 and inner lowerendplate 220 a include rounded surfaces, thereby allowing relativerotation between the inner lower endplate 220 a and outer lower endplate220 b. Additionally, the edges 225 of the inner lower endplate 220 a andthe mating slots 226 of the outer lower endplate 220 b do not includethe mating straight portions 227, 228 of the constrained embodiment.Thus, in the unconstrained embodiment of the two-piece prosthetic disc,as shown in FIGS. 19 and 20, the upper subassembly 205 is capable ofsubstantially free rotation relative to the outer lower endplate 220 b.

The two-piece structure embodiment of the prosthetic disc is implantedby a surgical procedure. After removing the natural disc, the outerlower endplate 220 b is placed onto and anchored into the inferiorvertebral body within the void between the two adjacent vertebral bodiespreviously occupied by the natural disc. Next, grooves are formed in thesuperior vertebral body. The upper subassembly 205 of the prostheticdisc is then inserted into the void, while aligning the anchoring fins211 with the grooves formed on the superior vertebral body, and whilesliding the inner lower endplate 220 a into the outer lower endplate 220b in a manner that the edges 225 of the inner endplate 220 a engage theslots 226 of the outer endplate 220 b. The anchoring fins cause theprosthetic disc to be secured in place between the adjacent vertebralbodies.

The two-piece prosthetic disc has several advantages over prior artartificial discs, as well as over alternative treatment procedures suchas spinal fusion. For example, the two-piece prosthetic discs describedherein provide compressive compliance similar to that of a naturalspinal disc. In addition, the motions in flexion, extension, lateralbending, and axial rotation are also restricted in a manner near oridentical to those associated with a natural disc.

C. Three-Piece Structure

A representative prosthetic intervertebral disc 300 having a three-piecestructure is shown in FIGS. 21 through 23. The prosthetic disc includesan upper endplate 310, a lower endplate 320, and a core assembly 330retained between the upper endplate 310 and the lower endplate 320.

The upper endplate 310 and lower endplate 320 are generally flat, planarmembers, and are fabricated from a physiologically acceptable materialthat provides substantial rigidity. Examples of materials suitable foruse in fabricating the upper endplate 310 and lower endplate 320 includetitanium, titanium alloys, stainless steel, cobalt/chromium, etc., whichare manufactured by machining or metal injection molding; plastics suchas polyethylene with ultra high molar mass (molecular weight) (UHMWPE),polyether ether ketone (PEEK), etc., which are manufactured by injectionmolding or compression molding; ceramics; graphite; and others.Optionally, the endplates may be coated with hydroxyapatite, titaniumplasma spray, or other coatings to enhance bony ingrowth.

As noted above, the upper and lower endplates typically have a length offrom about 12 mm to about 45 mm, preferably from about 13 mm to about 44mm, a width of from about 11 mm to about 28 mm, preferably from about 12mm to about 25 mm, and a thickness of from about 0.5 mm to about 4 mm,preferably from about 1 mm to about 3 mm. The sizes of the upper andlower endplates are selected primarily based upon the size of the voidbetween adjacent vertebral bodies to be occupied by the prosthetic disc.Accordingly, while endplate lengths and widths outside of the rangeslisted above are possible, they are not typical. The upper surface ofthe upper endplate 310 and the lower surface of the lower endplate 320are preferably each provided with a mechanism for securing the endplateto the respective opposed surfaces of the upper and lower vertebralbodies between which the prosthetic disc is to be implanted. Forexample, in FIGS. 21 and 23, the upper endplate 310 includes ananchoring fin 311. The anchoring fin 311 is intended to engage a matinggroove that is formed on the surface of the upper vertebral body tothereby secure the endplate to the vertebral body. The anchoring fin 311extends generally perpendicularly from the generally planar externalsurface of the upper endplate 310, i.e., upward from the upper side ofthe endplate as shown in FIGS. 21 and 23. As shown in the Figures, theanchoring fin 311 is disposed at the center of external surface of theupper endplate 310 and has a length that is slightly shorter than thewidth of the upper endplate 310. Although not shown in the Figures, theanchoring fin 311 may be provided with a plurality of serrations locatedon the top edge of the anchoring fin. The serrations are intended toenhance the ability of the anchoring fin to engage the vertebral bodyand to thereby secure the upper endplate 310 to the spine.

Similarly, the lower surface of the lower endplate 320 includes ananchoring fin 321. The anchoring fin 321 on the lower surface of thelower endplate 320 is identical in structure and function to theanchoring fin 311 on the upper surface of the upper endplate 310, withthe exception of its location on the prosthetic disc. The anchoring fin321 on the lower endplate 320 is intended to engage a mating grooveformed on the lower vertebral body, whereas the anchoring fin 311 on theupper endplate 310 is intended to engage a mating groove on the uppervertebral body. Thus, the prosthetic disc 300 is held in place betweenthe adjacent vertebral bodies.

Alternatively, the upper endplate 310 and lower endplate 320 of thethree-piece prosthetic disc may employ one of the alternative securingmechanisms shown in FIGS. 13A-C. As described above in relation to theone-piece prosthetic device shown in FIG. 13A, each of the upperendplate 110 and lower endplate 120 is provided with a single anchoringfin 111, 121. The anchoring fins 111, 121 are located along a centerline of the respective endplates, and each is provided with a pluralityof serrations 112, 122 on its upper edge. The single anchoring fins 111,121 are intended to engage grooves formed on the opposed surface of theupper and lower vertebral bodies, as described above. In FIG. 13B, eachof the upper endplate 110 and lower endplate 120 is provided with threeanchoring fins 111 a-c, 121 a-c. The FIG. 13B prosthetic disc is thesame as the prosthetic disc shown in FIG. 12, but it is shown inperspective rather than cross-section. Thus, the structure and functionof the anchoring fins 111 a-c and 121 a-c are as described above inrelation to FIG. 12. Finally, in FIG. 13C, each of the upper endplate110 and lower endplate 120 is provided with a plurality of serrations113, 123 over a portion of the exposed external surface of therespective endplate. The serrations 113, 123 are intended to engage theopposed surfaces of the adjacent vertebral bodies to thereby secure theendplates in place between the vertebral bodies. The serrations 113, 123may be provided over the entire external surface of each of the upperand lower endplates, or they may be provided over only a portion ofthose surfaces. For example, in FIG. 13C, the serrations 113 on theupper surface of the upper endplate 110 are provided over three majorareas, a first area 113 a near a first edge of the upper endplate 110, asecond area 113 b near the center of the upper endplate 110, and a thirdarea near a second edge of the endplate 113 c.

Turning to FIG. 54, in an optional embodiment, the anchoring fins 111are selectively retractable and extendable by providing a deploymentmechanism 160 that is associated with the upper endplate 110. A similarmechanism may be used on the lower endplate 120. The deploymentmechanism includes a slider 161 that slides within a channel 162 formedin the upper endplate 110. The channel 162 includes a threaded region163, and the slider 161 includes matching threads 164, thereby providinga mechanism for advancing the slider 161 within the channel 162. As theslider 161 is advanced within the channel 162, a tapered region 165engages the bottom surface of a deployable fin 166. Further advancementof the slider 161 causes the deployable fin 166 to be raised upwardwithin a slot 167 on the upper surface of the upper endplate 110.Reversing the deployment mechanism 160 causes the fin 166 to retract.The deployment mechanism 160 may also be used in conjunction withspikes, serrations, or other anchoring devices. In an alternativeembodiment, the threaded slider 161 of the deployment mechanism may bereplaced with a dowel pin that is advanced to deploy the fin 166. Otheradvancement mechanisms are also possible.

The core assembly 330 is intended to provide support to and to maintainthe relative spacing between the upper endplate 310 and lower endplate320. The core assembly 330 provides compressive compliance to thethree-piece prosthetic disc, as well as providing limited translation,flexion, extension, and lateral bending by and between the upperendplate 310 and lower endplate 320. The core assembly 330 furtherprovides substantially unlimited rotation by and between the upperendplate 310 and the lower endplate 320.

The core assembly 330 includes a top cap 331, a bottom cap 332, asidewall 333, and a core center 334 held by and retained between the topcap 331, bottom cap 332, and sidewall 333. The top cap 331 and bottomcap 332 are generally planar, and are fabricated from a physiologicallyacceptable material that provides substantial rigidity. Examples ofmaterials suitable for use in fabricating the top cap 331 and bottom cap332 include titanium, titanium alloys, stainless steel, cobalt/chromium,etc., which are manufactured by machining or metal injection molding;plastics such as polyethylene with ultra high molar mass (molecularweight) (UHMWPE), polyether ether ketone (PEEK), etc., which aremanufactured by injection molding or compression molding; ceramics;graphite; and others. The core center 334 is made of a relativelycompliant material, for example, polyurethane or silicone, and istypically fabricated by injection molding. The shape of the core center334 is typically generally cylindrical or bean-shaped, although theshape (as well as the materials making up the core center and the coremember size) may be varied to obtain desired physical or performanceproperties. For example, the core member 334 shape, size, and materialswill directly affect the degree of flexion, extension, lateral bending,and axial rotation of the prosthetic disc.

The top cap 331 and bottom cap 332 each preferably includes a generallyconcave indentation 336 formed at a center point of the cap. Theindentations 336 are intended to cooperate with a pair of retainersformed on the internal surfaces of the endplates to retain the coreassembly 330 in place between the retainers, as described more fullybelow.

The top cap 331 and bottom cap 332 preferably contain a plurality ofslots 335 spaced radially about the surface of each of the caps. One ormore fibers 340 are wound around the top cap 331 and bottom cap 332through the slots 335 to attach the endplates to one another. The fibers340 preferably are not tightly wound, thereby allowing a degree of axialrotation, bending, flexion, and extension by and between the top cap 331and bottom cap 332. The core center 334 is preferably pre-compressed.The actual number of slots 335 contained on each of the top cap 331 andbottom cap 332 is variable. Increasing the number of slots will resultin an increase in the circumferential density of the fibers holding theendplates together. Additionally, the fibers may be wound multiple timeswithin the same slot, thereby increasing the radial density of thefibers. In each case, this improves the wear resistance and increasesthe torsional and flexural stiffness of the prosthetic disc, therebyfurther approximating natural disc stiffness. In addition, the fibers340 may be passed through or wound on each slot, or only on selectedslots, as needed.

The purpose of the fibers 340 is to hold the top cap 331 and bottom cap332 together and to limit the range-of-motion to mimic therange-of-motion of a natural disc. Accordingly, the fibers preferablycomprise high tenacity fibers with a high modulus of elasticity, forexample, at least about 100 MPa, and preferably at least about 500 MPa.By high tenacity fibers is meant fibers that can withstand alongitudinal stress of at least 50 MPa, and preferably at least 250 MPa,without tearing. The fibers 140 are generally elongate fibers having adiameter that ranges from about 100 μm to about 500 μm, and preferablyabout 200 μm to about 400 μm. Optionally, the fibers may be injectionmolded with an elastomer to encapsulate the fibers, thereby providingprotection from tissue ingrowth and improving torsional and flexuralstiffness.

The fibers 340 may be fabricated from any suitable material. Examples ofsuitable materials include polyester (e.g., Dacron®), polyethylene,polyaramid, poly-paraphenylene terephthalamide (e.g., Kevlar®), carbonor glass fibers, polyethylene terephthalate, acrylic polymers,methacrylic polymers, polyurethane, polyurea, polyolefin, halogenatedpolyolefin, polysaccharide, vinylic polymer, polyphosphazene,polysiloxane, and the like.

The fibers 340 may be terminated on an endplate by tying a knot in thefiber on the superior surface of an endplate. Alternatively, the fibers340 may be terminated on an endplate by slipping the terminal end of thefiber into a slot on an edge of an endplate, similar to the manner inwhich thread is retained on a thread spool. The slot may hold the fiberwith a crimp of the slot structure itself, or by an additional retainersuch as a ferrule crimp. As a further alternative, tab-like crimps maybe machined into or welded onto the endplate structure to secure theterminal end of the fiber. The fiber may then be closed within the crimpto secure it. As a still further alternative, a polymer may be used tosecure the fiber to the endplate by welding. The polymer wouldpreferably be of the same material as the fiber (e.g., PE, PET, or theother materials listed above). Still further, the fiber may be retainedon the endplates by crimping a cross-member to the fiber creating aT-joint, or by crimping a ball to the fiber to create a ball joint.

The sidewall 333 is preferably made of polyurethane or silicone and maybe fabricated by injection molding, two-part component mixing, ordipping the core assembly into a polymer solution. Alternatively, anouter ring or gasket (not shown in the drawings) may optionally beprovided in place of the sidewall 333.

As noted above, the core assembly 330 is selectively retained betweenthe upper endplate 310 and the lower endplate 320. A preferred mechanismfor retaining the core assembly 330 between the two endplates isillustrated in FIGS. 21 through 23. For example, the upper endplate 310is provided with a retainer 313 formed on the interior surface of theupper endplate 310. The retainer 313 is a convex body formed at thecenter of the internal surface of the upper endplate 310 that extendsinto the space between the upper endplate 310 and lower endplate 320when the endplates are implanted into the patient. A similar retainer323 is formed on the opposed internal surface of the lower endplate 320.Each of the retainers 313, 323 is preferably of generally semi-sphericalshape, and each is preferably formed from the same material used tofabricate the upper and lower endplates 310, 320.

As shown, for example, in FIG. 23, the retainers 313, 323 formed on theinternal surfaces of the endplates cooperate with the indentations 336formed on the external surfaces of the top cap 331 and bottom 332 of thecore assembly 330 to hold the core assembly in place between theendplates. The amount of retaining force holding the core assembly 330in place will depend on several factors, including the materials used toform the endplates and the core assembly, the size and shape of the coreassembly, the distance separating the two endplates, the size and shapeof each of the retainers and indentations, and other factors. Any one orall of these factors may be varied to obtain desired results. Typically,the retaining force will be sufficient to hold the core assembly inplace, while still allowing each of the endplates to rotatesubstantially freely relative to the core assembly.

Turning to FIGS. 24A-C, three embodiments of the core assembly 330 areillustrated. In a first embodiment, shown in FIG. 24A, the core assembly330 is provided with a through hole 337, i.e., the central portion ofthe core assembly 330 is hollow. In this embodiment, although there areno indentations 336, the through hole 337 creates a shoulder 338 on eachof the top cap 331 and bottom cap 332. The shoulders 338 have a sizeselected to suitably engage the retainers 313, 323 formed on theendplates. In a second embodiment, the core assembly 330 is providedwith indentations 336 and the core center 334 extends throughout theinternal volume of the core assembly. Finally, in a third embodiment,the core assembly 330 is provided with indentations 336, but the corecenter 334 occupies only a central portion of the internal volume of thecore assembly 330.

Turning to FIGS. 25A-C, the core assembly may optionally include aplurality of reinforcing fibers 360 distributed throughout the body ofthe core assembly. The fibers 360 may be fabricated from any suitablematerial. Examples of suitable materials include polyester (e.g.,Dacron), polyethylene, polyaramid, carbon or glass fibers, polyethyleneterephthalate, acrylic polymers, methacrylic polymers, polyurethane,polyurea, polyolefin, halogenated polyolefin, polysaccharide, vinylicpolymer, polyphosphazene, polysiloxane, and the like. The reinforcingfibers 360 provide additional strength to the core assembly. The fiberreinforcement is made by injecting core center material around thefibers formed in the shape of the core center. Exemplary core shapes areshown in FIGS. 25A-C, and include a core assembly 330 having a throughhole 337 (FIG. 25A), a core assembly 330 having indentations 336 on eachof the top and bottom surfaces (FIG. 25B), and a core assembly 330having a toroidal shape (FIG. 25C).

The fibers 360 may be terminated on an endplate by tying a knot in thefiber on the superior surface of an endplate. Alternatively, the fibers360 may be terminated on an endplate by slipping the terminal end of thefiber into a slot on an edge of an endplate, similar to the manner inwhich thread is retained on a thread spool. The slot may hold the fiberwith a crimp of the slot structure itself, or by an additional retainersuch as a ferrule crimp. As a further alternative, tab-like crimps maybe machined into or welded onto the endplate structure to secure theterminal end of the fiber. The fiber may then be closed within the crimpto secure it. As a still further alternative, a polymer may be used tosecure the fiber to the endplate by welding. The polymer wouldpreferably be of the same material as the fiber (e.g., PE, PET, or theother materials listed above). Still further, the fiber may be retainedon the endplates by crimping a cross-member to the fiber creating aT-joint, or by crimping a ball to the fiber to create a ball joint.

Turning next to FIGS. 26, 27, and 28A-C, the core assembly mayoptionally be formed of stacks of reinforcing fabric having no silicone,polyurethane, or other polymeric component. As shown in FIG. 26, wovenfibers 370 are formed into sheets of fabric that are compressed into astack to form a core body. The woven fibers 370 may be formed ofmaterials such as polyester (e.g., Dacron), polyethylene, polyaramid,carbon or glass fibers, polyethylene terephthalate, acrylic polymers,methacrylic polymers, polyurethane, polyurea, polyolefin, halogenatedpolyolefin, polysaccharide, vinylic polymer, polyphosphazene,polysiloxane, and the like. FIG. 27 is a cross-sectional view of a wovenfiber core body. FIG. 28A illustrates a woven fiber core body 330 havinga through hole 337 similar to the structure described previously.Similarly, FIG. 28B illustrates a woven fiber core body 330 havingindentations 336 on its upper and lower surfaces. Finally, FIG. 28Cillustrates a woven fiber core body 330 having a toroidal shape.

The three-piece structure embodiment of the prosthetic disc is implantedby a surgical procedure. After removing the natural disc, grooves areformed in the superior and inferior vertebrae between which theprosthetic disc is to be implanted. The upper endplate 310 and lowerendplate 320 are then each implanted into the void, while aligning theanchoring fins 311321 with the grooves formed on the vertebral bodies.The anchoring fins cause the prosthetic disc to be secured in placebetween the adjacent vertebral bodies. After the upper endplate 310 andlower endplate 320 are implanted, the core assembly 330 is engagedbetween the endplates to complete the implantation.

The three-piece prosthetic disc has several advantages over prior artartificial discs, as well as over alternative treatment procedures suchas spinal fusion. For example, the prosthetic discs described hereinprovide compressive compliance similar to that of a natural spinal disc.In addition, the motions in flexion, extension, lateral bending, andaxial rotation are also restricted in a manner near or identical tothose associated with a natural disc.

D. Four-Piece Structure

Representative prosthetic intervertebral discs 400 having four-piecestructures are shown in FIGS. 29 through 35. The prosthetic discsinclude an upper endplate 410, a lower endplate 420, and a two-piececore assembly 430 retained between the upper endplate 410 and the lowerendplate 420.

The upper endplate 410 and lower endplate 420 are generally flat, planarmembers, and are fabricated from a physiologically acceptable materialthat provides substantial rigidity. Examples of materials suitable foruse in fabricating the upper endplate 410 and lower endplate 420 includetitanium, titanium alloys, stainless steel, cobalt/chromium, etc., whichare manufactured by machining or metal injection molding; plastics suchas polyethylene with ultra high molar mass (molecular weight) (UHMWPE),polyether ether ketone (PEEK), etc., which are manufactured by injectionmolding or compression molding; ceramics; graphite; and others.Optionally, the endplates may be coated with hydroxyapatite, titaniumplasma spray, or other coatings to enhance bony ingrowth.

As noted above, the upper and lower endplates typically have a length offrom about 12 mm to about 45 mm, preferably from about 13 mm to about 44mm, a width of from about 11 mm to about 28 mm, preferably from about 12mm to about 25 mm, and a thickness of from about 0.5 mm to about 4 mm,preferably from about 1 mm to about 3 mm. The sizes of the upper andlower endplates are selected primarily based upon the size of the voidbetween adjacent vertebral bodies to be occupied by the prosthetic disc.Accordingly, while endplate lengths and widths outside of the rangeslisted above are possible, they are not typical

The upper surface of the upper endplate 410 and the lower surface of thelower endplate 420 are preferably each provided with a mechanism forsecuring the endplate to the respective opposed surfaces of the upperand lower vertebral bodies between which the prosthetic disc is to beimplanted. For example, as shown in FIGS. 30 and 32, the upper endplate410 includes an anchoring fin 411. The anchoring fin 411 is intended toengage a mating groove that is formed on the surface of the uppervertebral body to thereby secure the endplate to the vertebral body. Theanchoring fin 411 extends generally perpendicularly from the generallyplanar external surface of the upper endplate 410, i.e., upward from theupper side of the endplate as shown in FIGS. 30 and 32. As shown in theFigures, the anchoring fin 411 is disposed at the center of externalsurface of the upper endplate 410 and has a length that is slightly lessthan the width of the upper endplate 410. Although not shown in theFigures, the anchoring fin 411 may be provided with a plurality ofserrations located on its top edge. The serrations are intended toenhance the ability of the anchoring fin to engage the vertebral bodyand to thereby secure the upper endplate 410 to the spine.

Similarly, the lower surface of the lower endplate 420 includes ananchoring fin 421. The anchoring fin 421 on the lower surface of thelower endplate 420 is identical in structure and function to theanchoring fin 411 on the upper surface of the upper endplate 410, withthe exception of its location on the prosthetic disc. The anchoring fin421 on the lower endplate 420 is intended to engage a mating grooveformed on the lower vertebral body, whereas the anchoring fin 411 on theupper endplate 410 is intended to engage a mating groove on the uppervertebral body. Thus, the prosthetic disc 400 is held in place betweenthe adjacent vertebral bodies.

Alternatively, the upper endplate 410 and lower endplate 420 of thethree-piece prosthetic disc may employ one of the alternative securingmechanisms shown in FIGS. 13A-C. As described above in relation to theone-piece prosthetic device shown in FIG. 13A, each of the upperendplate 110 and lower endplate 120 is provided with a single anchoringfin 111, 121. The anchoring fins 111, 121 are located along a centerlineof the respective endplates, and each is provided with a plurality ofserrations 112, 122 on its upper edge. The single anchoring fins 111,121 are intended to engage grooves formed on the opposed surface of theupper and lower vertebral bodies, as described above. In FIG. 13B, eachof the upper endplate 110 and lower endplate 120 is provided with threeanchoring fins 111 a-c, 121 a-c. The FIG. 13B prosthetic disc is thesame as the prosthetic disc shown in FIG. 12, but it is shown inperspective rather than cross-section. Thus, the structure and functionof the anchoring fins 111 a-c and 121 a-c are as described above inrelation to FIG. 12. Finally, in FIG. 13C, each of the upper endplate110 and lower endplate 120 is provided with a plurality of serrations113, 123 over a portion of the exposed external surface of therespective endplate. The serrations 113, 123 are intended to engage theopposed surfaces of the adjacent vertebral bodies to thereby secure theendplates in place between the vertebral bodies. The serrations 113, 123may be provided over the entire external surface of each of the upperand lower endplates, or they may be provided over only a portion ofthose surfaces. For example, in FIG. 13C, the serrations 113 on theupper surface of the upper endplate 110 are provided over three majorareas, a first area 113 a near a first edge of the upper endplate 110, asecond area 113 b near the center of the upper endplate 110, and a thirdarea near a second edge of the endplate 113 c.

Turning to FIG. 54, in an optional embodiment, the anchoring fins 111are selectively retractable and extendable by providing a deploymentmechanism 160 that is associated with the upper endplate 110. A similarmechanism may be used on the lower endplate 120. The deploymentmechanism includes a slider 161 that slides within a channel 162 formedin the upper endplate 110. The channel 162 includes a threaded region163, and the slider 161 includes matching threads 164, thereby providinga mechanism for advancing the slider 161 within the channel 162. As theslider 161 is advanced within the channel 162, a tapered region 165engages the bottom surface of a deployable fin 166. Further advancementof the slider 161 causes the deployable fin 166 to be raised upwardwithin a slot 167 on the upper surface of the upper endplate 110.Reversing the deployment mechanism 160 causes the fin 166 to retract.The deployment mechanism 160 may also be used in conjunction withspikes, serrations, or other anchoring devices. In an alternativeembodiment, the threaded slider 161 of the deployment mechanism may bereplaced with a dowel pin that is advanced to deploy the fin 166. Otheradvancement mechanisms are also possible.

FIG. 29 illustrates yet another alternative mechanism for securing theupper and lower endplates to the vertebral bodies. As shown in theFigure, the upper endplate 410 may be provided with a plurality ofanchoring spikes 419 spaced over the external surface of the endplate.The anchoring spikes 419 are adapted to engage the internal surface ofthe vertebral body. Although not shown in FIG. 29, the external surfaceof the lower endplate 420 may optionally be provided with similaranchoring spikes to secure the lower endplate to the internal surface ofthe inferior vertebral body.

The core assembly 430 is intended to provide support to and to maintainthe relative spacing between the upper endplate 410 and lower endplate420. The core assembly 430 provides compressive compliance to thefour-piece prosthetic disc, as well as providing limited translation,flexion, extension, and lateral bending by and between the upperendplate 410 and lower endplate 420. The core assembly 430 furtherprovides substantially unlimited rotation by and between the upperendplate 410 and the lower endplate 420.

The core assembly 430 includes an upper core member 430 a and a lowercore member 430 b, 430 c. Two embodiments of the core assembly 430 ofthe four-piece prosthetic disc are shown in FIGS. 29 through 35. In thefirst embodiment, shown in FIGS. 29 through 32, both the upper coremember 430 a and the lower core member 430 b include a core structurehaving top and bottom caps, slots, fibers, a core center, and an annularcapsule. In the second embodiment, shown in FIGS. 33 through 35, theupper core member 430 a is identical to that of the first embodiment,but the lower core member 430 c is, instead, a solid structure. Thesestructures are described more fully below.

The upper core member 430 a includes a top cap 431 a, a bottom cap 432a, a sidewall 433 a, and a core center 434 a held by and retainedbetween the top cap 431 a, bottom cap 432 a, and sidewall 433 a. The topcap 431 a and bottom cap 432 a are generally planar, and are fabricatedfrom a physiologically acceptable material that provides substantialrigidity. Examples of materials suitable for use in fabricating the topcap 431 a and bottom cap 432 a include titanium, titanium alloys,stainless steel, cobalt/chromium, etc., which are manufactured bymachining or metal injection molding; plastics such as polyethylene withultra high molar mass (molecular weight) (UHMWPE), polyether etherketone (PEEK), etc., which are manufactured by injection molding orcompression molding; ceramics; graphite; and others. The core center 434a is made of a relatively compliant material, for example, polyurethaneor silicone, and is typically fabricated by injection molding. The shapeof the core center 434 a is typically generally cylindrical orbean-shaped, although the shape (as well as the materials making up thecore center and the core member size) may be varied to obtain desiredphysical or performance properties. For example, the core member 434 ashape, size, and materials will directly affect the degree of flexion,extension, lateral bending, and axial rotation of the prosthetic disc.

The bottom cap 432 a preferably includes a generally convex retainer 437a formed at a center point of the bottom cap 432 a. The retainer 437 ais intended to cooperate with an indentation 436 b, 436 c formed on theupper surface of the lower core member 430 b, 430 c to create anengagement between the upper core member 430 a and the lower core member430 b, 430 c, as described more fully below.

The top cap 431 a and bottom cap 432 a preferably contain a plurality ofslots 435 a spaced radially about the surface of each of the caps. Oneor more fibers 440 are wound around the top cap 431 a and bottom cap 432a through the slots 435 a to attach the top and bottom caps to oneanother. The fibers 440 preferably are not tightly wound, therebyallowing a degree of axial rotation, bending, flexion, and extension byand between the top cap 431 a and bottom cap 432 a. The core center 434a is preferably pre-compressed. The actual number of slots 435 acontained on each of the top cap 431 a and bottom cap 432 a is variable.Increasing the number of slots will result in an increase in thecircumferential density of the fibers holding the endplates together.Additionally, the fibers may be wound multiple times within the sameslot, thereby increasing the radial density of the fibers. In each case,this improves the wear resistance and increases the torsional andflexural stiffness of the prosthetic disc, thereby further approximatingnatural disc stiffness. In addition, the fibers 440 may be passedthrough or wound on each slot, or only on selected slots, as needed.

The purpose of the fibers 440 is to hold the top cap 431 a and bottomcap 432 a together and to limit the range-of-motion to mimic therange-of-motion of a natural disc. Accordingly, the fibers preferablycomprise high tenacity fibers with a high modulus of elasticity, forexample, at least about 100 MPa, and preferably at least about 500 MPa.By high tenacity fibers is meant fibers that can withstand alongitudinal stress of at least 50 MPa, and preferably at least 250 MPa,without tearing. The fibers 440 are generally elongate fibers having adiameter that ranges from about 100 μm to about 500 μm, and preferablyabout 200 μm to about 400 μm. Optionally, the fibers may be injectionmolded with an elastomer to encapsulate the fibers, thereby providingprotection from tissue ingrowth and improving torsional and flexuralstiffness.

The fibers 440 may be fabricated from any suitable material. Examples ofsuitable materials include polyester (e.g., Dacron®), polyethylene,polyaramid, poly-paraphenylene terephthalamide (e.g., Kevlar®), carbonor glass fibers, polyethylene terephthalate, acrylic polymers,methacrylic polymers, polyurethane, polyurea, polyolefin, halogenatedpolyolefin, polysaccharide, vinylic polymer, polyphosphazene,polysiloxane, and the like.

The fibers 440 may be terminated on an endplate by tying a knot in thefiber on the superior surface of an endplate. Alternatively, the fibers440 may be terminated on an endplate by slipping the terminal end of thefiber into a slot on an edge of an endplate, similar to the manner inwhich thread is retained on a thread spool. The slot may hold the fiberwith a crimp of the slot structure itself, or by an additional retainersuch as a ferrule crimp. As a further alternative, tab-like crimps maybe machined into or welded onto the endplate structure to secure theterminal end of the fiber. The fiber may then be closed within the crimpto secure it. As a still further alternative, a polymer may be used tosecure the fiber to the endplate by welding. The polymer wouldpreferably be of the same material as the fiber (e.g., PE, PET, or theother materials listed above). Still further, the fiber may be retainedon the endplates by crimping a cross-member to the fiber creating aT-joint, or by crimping a ball to the fiber to create a ball joint.

The sidewall 433 a is preferably made of polyurethane or silicone andmay be fabricated by injection molding, two-part component mixing, ordipping the core assembly into a polymer solution. Alternatively, anouter ring or gasket (not shown in the drawings) may optionally beprovided in place of the sidewall 433 a.

As shown, for example, in FIGS. 29 through 35, the top cap 431 a of theupper core member 430 a includes an edge member 438 a that is adapted toengage a groove 416 formed on the perimeter of the internal surface ofthe upper endplate 410 to provide an engagement mechanism for attachingthe upper core member 430 a to the upper endplate 410. For example, theupper core member 430 a is slid into the upper endplate 410, as shown bythe arrows in FIG. 29. After the upper endplate 430 a is fully advanced,i.e., once the leading edge of the edge member 438 a contacts theinterior of the groove 416 on the upper endplate 410, a tab 461 a on theupper surface of the top cap 431 a engages a slot 462 a on the lowersurface of the upper endplate 410 (see FIGS. 30 and 33), thereby lockingthe upper core member 430 a in place within the upper endplate 410.

Turning to the first embodiment of the lower core member 430 b, shown inFIGS. 29 through 32, the lower core member 430 b includes a top cap 431b, a bottom cap 432 b, a sidewall 433 b, and a core center 434 b held byand retained between the top cap 431 b, bottom cap 432 b, and sidewall433 b. The top cap 431 b and bottom cap 432 b are generally planar, andare fabricated from a physiologically acceptable material that providessubstantial rigidity. Examples of materials suitable for use infabricating the top cap 431 b and bottom cap 432 b include titanium,titanium alloys, stainless steel, cobalt/chromium, etc., which aremanufactured by machining or metal injection molding; plastics such aspolyethylene with ultra high molar mass (molecular weight) (UHMWPE),polyether ether ketone (PEEK), etc., which are manufactured by injectionmolding or compression molding; ceramics; graphite; and others. The corecenter 434 b is made of a relatively compliant material, for example,polyurethane or silicone, and is typically fabricated by injectionmolding. The shape of the core center 434 b is typically generallycylindrical or bean-shaped, although the shape (as well as the materialsmaking up the core center and the core member size) may be varied toobtain desired physical or performance properties. For example, the coremember 434 b shape, size, and materials will directly affect the degreeof flexion, extension, lateral bending, and axial rotation of theprosthetic disc.

The top cap 431 b preferably includes a generally concave indentation436 b formed at a center-point of the top cap 431 b. The indentation 436b is intended to cooperate with the retainer 437 a formed on the lowersurface of the upper core member 430 a to create an engagement betweenthe upper core member 430 a and the lower core member 430 b, asdescribed more fully below.

The top cap 431 b and bottom cap 432 b preferably contain a plurality ofslots 435 b spaced radially about the surface of each of the caps. Oneor more fibers 440 are wound around the top cap 431 b and bottom cap 432b through the slots 435 b to attach the top and bottom caps to oneanother. The fibers 440 preferably are not tightly wound, therebyallowing a degree of axial rotation, bending, flexion, and extension byand between the top cap 431 b and bottom cap 432 b. The core center 434b is preferably pre-compressed. The actual number of slots 435 bcontained on each of the top cap 431 b and bottom cap 432 b is variable.In addition, the fibers 440 may be passed through or wound on each slot,or only on selected slots, as needed.

The purpose of the fibers 440 is to hold the top cap 431 b and bottomcap 432 b together. Accordingly, the fibers preferably comprise hightenacity fibers with a high modulus of elasticity, for example, at leastabout 100 MPa, and preferably at least about 500 MPa. By high tenacityfibers is meant fibers that can withstand a longitudinal stress of atleast 50 MPa, and preferably at least 250 MPa, without tearing. Thefibers 440 are generally elongate fibers having a diameter that rangesfrom about 100 μm to about 500 μm, and preferably about 200 μm to about400 μm.

The fibers 440 may be fabricated from any suitable material. Examples ofsuitable materials include polyester (e.g., Dacron), polyethylene,polyaramid, carbon or glass fibers, polyethylene terephthalate, acrylicpolymers, methacrylic polymers, polyurethane, polyurea, polyolefin,halogenated polyolefin, polysaccharide, vinylic polymer,polyphosphazene, polysiloxane, and the like.

The sidewall 433 b is preferably made of polyurethane or silicone andmay be fabricated by injection molding, two-part component mixing, ordipping the core assembly into a polymer solution. Alternatively, anouter ring or gasket (not shown in the drawings) may optionally beprovided in place of the sidewall 433 b.

As shown, for example, in FIGS. 29 through 32, the bottom cap 432 b ofthe lower core member 430 b includes an edge member 438 b that isadapted to engage a groove 426 formed on the perimeter of the internalsurface of the lower endplate 420 to provide an engagement mechanism forattaching the lower core member 430 b to the lower endplate 420. Forexample, the lower core member 430 b is slid into the lower endplate420, as shown by the arrow in FIG. 16. After the lower endplate 430 b isfully advanced, i.e., once the leading edge of the edge member 438 bcontacts the interior of the groove 426 on the lower endplate 420, a tab461 b on the lower surface of the bottom cap 432 b engages a slot 462 bon the upper surface of the lower endplate 420 (see FIG. 30), therebylocking the lower core member 430 b in place within the lower endplate420.

Turning to the second embodiment of the lower core member 430 c, shownin FIGS. 33 through 35, the lower core member 430 c is formed of a solidstructure having none of the top and bottom caps, sidewall, core center,or fibers that are included in the first embodiment of the lower coremember 430 b. The second embodiment of the lower core member 430 c hasan identical external shape and size to that of the first embodiment ofthe lower core member 430 b, including having an edge member 438 c thatengages the groove 426 on the internal surface of the lower endplate420. A tab 461 c is configured to selectively engage the notch 462 cformed on the upper internal surface of the lower endplate 420. Anindentation 436 c is formed on the central upper surface of the lowercore member 430 c, and is adapted to engage the retainer 437 a formed onthe upper core member 430 a.

Examples of materials suitable for use in fabricating the secondembodiment of the lower core member 430 c include titanium, titaniumalloys, stainless steel, cobalt/chromium, etc., which are manufacturedby machining or metal injection molding; plastics such as polyethylenewith ultra high molar mass (molecular weight) (UHMWPE), polyether etherketone (PEEK), etc., which are manufactured by injection molding orcompression molding; ceramics; graphite; and others.

The four-piece structure embodiment of the prosthetic disc is implantedby a surgical procedure. After removing the natural disc, grooves areformed in the superior and inferior vertebrae between which theprosthetic disc is to be implanted (only in the situation where theendplates are provided with anchoring fins). The upper endplate 410 andlower endplate 420 are then each implanted into the void, while aligningthe anchoring fins 411, 421 with the grooves formed on the vertebralbodies. The anchoring fins cause the prosthetic disc to be secured inplace between the adjacent vertebral bodies. After the upper endplate410 and lower endplate 420 are put in position, the core assembly 430 isengaged between the endplates to complete the implantation.

The four-piece prosthetic disc has several advantages over prior artartificial discs, as well as over alternative treatment procedures suchas spinal fusion. For example, the prosthetic discs described hereinprovide compressive compliance similar to that of a natural spinal disc.In addition, the motions in flexion, extension, lateral bending, andaxial rotation are also restricted in a manner near or identical tothose associated with a natural disc.

E. Fabric Tubes

The one-piece, two-piece, three-piece, and four-piece structures of theprosthetic discs described above include upper and lower endplates thatare attached to each other by fibers wound around the endplates. In analternative embodiment, the fiber component is provided in a fabriccylinder or tubing of woven or knitted form, rather than as individualfibers. The fabric tubing extends between and structurally connects theupper and lower endplates.

In a first example, a single fabric tube may be provided in place of thewound fibers. The fabric tube may be attached at its upper edge to theupper endplate, and at its lower edge to the lower endplate. Forexample, through-holes may be provided in each of the endplates to allowthe fabric tubing (or individually woven fibers) to pass through and tobe secured by knots or crimping on the external surfaces of theendplates. Alternatively, the fabric tube may be attached to eachendplate by a peripheral metal or plastic ring that is fixed to theinterior surfaces of the endplates.

In another example, two or more tubes of fabric may be provided betweenand interconnecting the upper and lower endplates. The two or morefabric tubes may be attached to the endplates by through-holes, asdescribed above, or by press-fit, adhesion, weld, or injection moldingintegration to a progressively smaller metal or plastic ring with tubingcircumferentially affixed to it. This structure creates an assembly oftwo or more concentric layers of fabric tubing. Alternatively, theconcentric tubes may be terminated by collecting each tubing endtogether and crimping or sewing them together, then fixing the collectedends to the upper and lower endplates. As a still further alternative,an injection molded lid may be fabricated in a manner in which the lidcaptures the terminal ends of each of the fabric tubes during theinjection molding process.

In a particularly preferred embodiment, multiple concentric fabric tubesare provided. Each of the fabric tubes may be formed from a fabric ofmaterial different from the other tubes (e.g, PET, PE, PTFE, Polyamide,etc.), or from a fabric having different material properties. Thisprovides the ability to construct prosthetic discs having a range ofperformance characteristics.

As an alternative, the tubing may be comprised of a fiber reinforcedelastomeric material rather than a fabric alone. For example, apolyurethane, PDMS, polyester, or other elastomer may be integrated witha fabric or with individual fibers to create a tubing that attaches andinterconnects the upper and lower endplates.

F. Anti-Creep Compression Member

Turning to FIG. 53, an optional anti-creep compression member 135 isshown. The anti-creep member 135 is intended to prevent “creeping” ofthe core due to vertical compression and lateral expansion of the core,which occurs due to extended from wear. The anti-creep member 135 ispreferably used in connection with a toroidal shaped core member 130,230, 330, 430 of any of the one-, two-, three-, or four-piece structuresof the prosthetic disc. The anti-creep element 135 includes a post 136extending downward from the upper endplate 110, 210, 310, 410 and amating receptacle or cup 137 extending upward from the lower endplate120, 220, 320, 420. Alternatively, the post 136 may extend upward fromthe lower endplate and the receptacle 137 may extend downward from theupper endplate. A spring 138 is located within the receptacle 138. Thepost 136 is slightly conical in shape, and the receptacle 137 has aslightly larger diameter than the post 136 in order to receive the post136 within the receptacle 137. The slightly conical shapes of the post136 and cup 137 are preferred in order to accommodate lateral bending(side-to-side), flexion (forward), and extension (backward) of the upperand lower endplates relative to one another. The spring is pre-loaded toprovide a force biasing the two endplates apart.

G. Advantages of the Present Prosthetic Intervertebral Discs

It is evident from the above discussion and results that the presentinvention provides significantly improved prosthetic intervertebraldiscs. Significantly, the subject discs closely imitate the mechanicalproperties of the fully functional natural discs that they are intendedto replace.

More specifically, the modes of spinal motion may be characterized ascompression, shock absorption (i.e., very rapid-compressive loading andunloading), flexion (forward) and extension (backward), lateral bending(side-to-side), torsion (twisting), and translation and sublaxation(motion of axis). The prosthetic discs described herein semi-constraineach mode of motion, rather than completely constrain or allow a mode tobe unconstrained. In this manner, the present prosthetic discs closelymimic the performance of natural discs. The tables below provide datathat illustrates this performance. TABLE 1 One-Piece Structure LumbarProsthetic Disc Compared to Natural Human Disc and Ball & Socket DesignProsthetic Disc Compressive Mode of Motion Prosthetic Prosthetic HumanBall & Socket Disc Core Disc Core & Properties Spine Design Only FiberStiffness ≈1288 Very large 800-1600 850-1650 (N/mm) ROM (mm) 0.50 ≈00.61 0.50 Ult. Load (N) 3952 >5900 >5900 >5900

TABLE 2 One-Piece Structure Cervical Prosthetic Disc Compared to NaturalHuman Disc and Ball & Socket Design Prosthetic Disc Compressive Mode ofMotion Prosthetic Prosthetic Human Ball & Socket Disc Core Disc Core &Properties Spine Design Only Fiber Stiffness ≈737 Very large 100-950150-1000 (N/mm) ROM (mm) 0.70 +/− 0.03 ≈0 ≈0.87 ≈0.60 Ult. Load≈1600 >5900 >9000 >9000 (N)

The subject discs exhibit stiffness in the axial direction, torsionalstiffness, bending stiffness in the saggital plane, and bendingstiffness in the front plane, where the degree of these features can becontrolled independently by adjusting the components of the discs. Theinterface mechanism between the endplates and the core members ofseveral embodiments of the described prosthetic discs enables a veryeasy surgical operation. In view of the above and other benefits andfeatures provided by the subject inventions, it is clear that thesubject inventions represent a significant contribution to the art.

II. Implantation Apparatus and Methods

A. Conventional (Non-Minimally Invasive Method)

The prosthetic intervertebral discs may be implanted into a patient'sspine using the apparatus and methods described herein. This descriptionwill focus on use of apparatus to implant one- and two-piece prostheticdiscs, although the apparatus may also be used to implant otherembodiments of the prosthetic disc with little or no modification, aswill be appreciated by a person of skill in the art. In addition, and asdescribed below, the method may incorporate less than all of theapparatus components described below.

The prosthetic discs are implanted surgically between two adjacentvertebrae, an upper vertebra and a lower vertebra, in a patient's spinalcolumn. The vertebrae to be treated are exposed using conventionalsurgical procedures. After exposure, the natural vertebral disc isremoved, leaving a void space between the two adjacent vertebrae. Theprosthetic intervertebral disc is then implanted using the apparatus andmethods described below.

1. Implantation Tools

In a first embodiment, and in reference to FIGS. 36-38, the implantationtools include a spacer 810, a two-sided chisel 830, and a holder 850.

Turning first to FIGS. 36A-B, the spacer 810 includes a proximal handle812, a shaft 814, and a head portion 816. The handle 812 is adapted tobe easily grasped by the user during the implantation procedure. Theshaft 814 is preferably cylindrical and smaller in cross-section thanthe handle. The head portion 816 has a size and shape adapted to performits function of being inserted between and separating two adjacentvertebral bodies. In the embodiment shown in the Figures, the headportion 816 has a generally trapezoidal shape when viewed from above orbelow, with a leading edge 817 being generally parallel to, but having ashorter length than the trailing edge 818. Other shapes may be used. Thehead portion has a thickness “h”. The thickness “h” may be variedaccording to need, i.e., the thickness “h” will impact the ability ofthe user to insert the head portion 816 between the two vertebralbodies, and also the amount by which the head portion 816 will be ableto separate the two bodies. Thus, a spacer 810 with a head portion 816of relatively large or small thickness “h” may be used depending on theneed. The edges 819 of the head portion 816 are generally rounded toallow the head portion 816 to be more easily inserted between the twovertebral bodies.

Turning next to FIGS. 37A-B, the two-sided chisel 830 includes a handle832, a shaft 834, and a head portion 836. The handle 832 is adapted tobe easily grasped by the user during the implantation procedure. Theshaft 834 is preferably cylindrical and smaller in cross-section thanthe handle. The head portion 836 has a size and shape adapted to performits function of being inserted between and creating grooves on the twoadjacent vertebral bodies. In the embodiment shown in the Figures, thehead portion 836 has a generally trapezoidal shape when viewed fromabove or below, with a leading edge 837 being generally parallel to, buthaving a shorter length than the trailing edge 838. Other shapes may beused. The head portion has a thickness “h”. The thickness “h” may bevaried according to need, i.e., the thickness “h” will impact theability of the user to be able to insert the head portion 836 betweenthe two vertebral bodies and to cut grooves on the two bodies. Thus, achisel 830 with a head portion 836 of relatively large or smallthickness “h” may be used depending on the need.

The chisel 830 includes a plurality of wedge-shaped blades 839 formed onthe upper and lower surfaces of the head portion 836. The blades 839 ofthe chisel 830 are adapted to create grooves in the lower surface of theupper vertebra and on the upper surface of the lower vertebra beingtreated. In the embodiment shown in the Figures, the chisel 830 includesthree blades 839 on each of the upper and lower surfaces. More or fewerblades may be provided. Optimally, the number, shape, and orientation ofthe blades 839 on the surfaces of the chisel 830 are selected to matchthose of the anchoring fins provided on the surfaces of the prostheticdisc to be implanted.

Turning next to FIGS. 38A-B, the holder 850 includes a handle 852, ashaft 854, and a head portion 856. The handle 852 is adapted to beeasily grasped by the user during the implantation procedure. The shaft854 is preferably cylindrical and smaller in cross-section than thehandle. The head portion 856 has a size and shape adapted to perform itsfunction of retaining the prosthetic disc on an end thereof in order toimplant the disc between the two adjacent vertebral bodies.

The head portion 856 of the holder 850 includes a proximal body portion857 and two arms 858 a-b extending distally from the body portion 857.The body portion 857 has a generally square shape, and its distal endincludes a slightly concave section 859 at its center that provides aspace for receiving a portion of the prosthetic disc. Each of the arms858 a-b also includes a slightly recessed portion 860 a-b that isadapted to engage the side surfaces of the prosthetic disc in order tofacilitate holding the disc in place during the implantation procedure.The body portion also includes engagement pins 861 on its distalsurface, which engagement pins 861 are adapted to engage mating holesprovided on the prosthetic disc.

In an alternative embodiment, and in reference to FIGS. 39-42, theimplantation tools include a guide 500, a lower pusher 520 connected toa first chisel 540, an upper endplate holder 560, and a second chisel580.

Turning first to FIG. 39, the guide 500 serves the purposes of, first,positioning and retaining the lower endplate 220 b in place on the lowerof the two adjacent vertebrae being treated, and, second, guiding one ormore of the other implantation tools to their proper locations forperforming their functions. In the preferred embodiment, the guide 500comprises a generally flat, elongated member 501 having a first end 502,a second end 503, and a pair of raised sides 504, 505. Each of theraised sides 504, 505 includes an inwardly facing portion 504 a, 505 athat extends back over the elongated member 501 on a plane slightlyabove that of the elongated member. Each of the inwardly facing portions504 a, 505 a of the pair of raised sides 504, 505 thereby forms a groove506, 507 that extends along the length of the guide 500. As describedbelow, the grooves 506, 507 may be used to guide one or more of theother implantation tools in cooperation with a flange provided on thoseother tools.

Extending from the first end 502 of the guide 500 are a pair of lowerendplate rods 508, 509. Each of the lower endplate rods 508, 509 is agenerally cylindrical rod that extends outward from the first end 502 ofthe guide 500 in the plane of the elongate member 501 or parallel tothat plane. The sizes of the lower endplate rods 508, 509—e.g., lengths,cylindrical diameters—are not critical, provided that the rods are ofsufficient size to be capable of performing the function of engaging andretaining the lower endplate 220 b, as described more fully below.

Turning to FIG. 40, in the preferred embodiment, a spacer tool 570includes a combination of a lower pusher 520 and a first chisel 540attached to a base member 530. The lower pusher 520 includes a pair oflower pusher rods 521 a, 521 b. Each of the lower pusher rods 521 a, 521b is connected at a first end to the base 530. At a second end, across-member 522 extends between and connects to each of the pair oflower pusher rods 521 a, 521 b. The two lower pusher rods 521 a, 521 bare thus held in a generally parallel relation to one another and extendoutward from the base 530. At the end opposite the base 530, each of thelower pusher rods 521 a, 521 b is attached to a lower endplate insert523. The lower endplate insert 523 includes a flange 524 along its edgethat is adapted to engage the matching slot 226 found on an outer lowerendplate 220 b of a two-piece prosthetic disc, such as those describedherein.

In the preferred embodiment, each of the lower pusher rods 521 a, 521 band the cross-member 522 are generally cylindrical rods. Thecross-sectional shape and size of the rods are not critical, such thatthe lower pusher rods 521 a, 521 b are capable of advancing the lowerendplate during the implantation procedure, as described more fullybelow.

In the preferred embodiment illustrated in FIG. 40, the base 530includes a block-shaped bottom portion 531. The bottom portion 531 ofthe base 530 is the portion of the base to which the pusher rods 521 a,521 b of the lower pusher 520 are attached. The bottom portion 531 shownin FIG. 40 has a generally block-shaped body, although the size andshape of the bottom portion 531 are not critical.

Extending upward from the top surface of the bottom portion are twoflanges, a tall flange 532 and a short flange 533. A pivot pin 534 islocated at the upper end of the tall flange 532. The pivot pin 534extends through a hole in the upper end of the tall flange 532, and isable to rotate around its pivot axis. A pair of upper pusher rods 541 a,541 b are attached to the pivot pin 534, with one of the two upperpusher rods 541 a attached to a first end of the pivot pin 534, and theother upper pusher rod 541 b attached to the opposite end of the pivotpin 534. At the end of the upper pusher rods 541 a, 541 b opposite thepivot pin 534, the upper pusher rods 541 a, 541 b are attached to afirst chisel 540. In addition, a cross-member 542 attaches to andinterconnects the pair of upper pusher rods 541 a, 541 b near the end towhich the first chisel 540 is attached.

A ratchet key 535 is extends through a hole in the short flange 533. Theratchet key 535 is able to rotate around its longitudinal axis withinthe hole in the short flange. The ratchet key 535 includes a graspingportion 536 extending from one side of the short flange 533, and a gearportion (not shown in the Figures) extending from the opposite side ofthe short flange 533. An elongated guide rail 537 extends beneath thegear portion of the ratchet key 535 and generally between the pair ofupper pusher rods 541 a, 541 b and the pair of lower pusher rods 521 a,521 b. The guide rail 537 includes a plurality of teeth 538 formed onits upper side, which teeth are adapted to engage the gear portion ofthe ratchet key 535. Thus, by rotating the ratchet key 535, a user isable to advance or withdraw the guide rail 537.

A separator 515 is attached to an end of the guide rail 537. Theseparator 515 is a generally flat member that is disposed generallytransversely to the guide rail 537. A pair of upper grooves 516 a, 516 bare formed on the top edge of the separator 515. The upper grooves 516a, 516 b have a size and are located so as to slidably engage the upperpusher rods 541 a, 541 b. Similarly, a pair of lower grooves 517 a, 517b are formed on the bottom edge of the separator 515. The lower grooves517 a, 517 b have a size and are located so as to slidably engage thelower pusher rods 521 a, 521 b. Thus, as shown in FIG. 40, the separatoris able to be advanced or withdrawn along the lengths of the upperpusher rods 541 a, 541 b and lower pusher rods 521 a, 521 b by turningthe ratchet key 535. Turning the ratchet key 535 causes the gear portionof the ratchet key 535 to engage the teeth 538 on the guide rail 537.With reference to the perspective illustrated in FIG. 40, rotating theratchet key clockwise will cause the guide rail 537 and the separator515 to withdraw, i.e., to draw nearer to the base 530. Alternatively,rotating the ratchet key 535 counter-clockwise will cause the guide rail537 and the separator to advance, i.e., to move away from the base 530.

As best seen in the illustration in FIG. 40, the separator 515 has apartial height, h, that is defined as the distance between the bottomedge of the upper grooves 516 a, 516 b and the top edge of the lowergrooves 517 a, 517 b. The partial height h of the separator 515 is lessthan the distance separating the upper pusher rods 541 a, 541 b andlower pusher rods 521 a, 521 b at the point that they attach to the base530. The partial height h of the separator is greater than the height ofthe prosthetic disc or, stated otherwise, the partial height h of thespacer is greater than the post-operative distance separating the twoadjacent vertebrae being treated. Thus, as explained more fully below,the separator 515 has a partial height h that is suitable for expandingthe distance separating the first chisel 540 and the lower endplateinsert 523 as the separator 515 is advanced during the implantationprocedure.

The first chisel 540 is attached to the ends of each of the upper pusherrods 541 a, 541 b opposite the tall flange 532. The first chisel 540includes a generally flat plate portion 543 and one or more wedge-shapedblades 544 extending upward from the flat plate portion 543. The blades544 of the first chisel are adapted to create grooves in the lowersurface of the upper vertebra being treated. The flat plate portion 543of the first chisel is preferably relatively thin in relation to theheight of the prosthetic disc, thereby allowing the first chisel to beinserted between the two adjacent vertebrae after the natural disc hasbeen removed.

Turning to FIG. 41, the upper endplate holder 560 includes a pusherblock 561 attached to the end of a push rod 563. The pusher block 561has a generally flat front surface 562 that is adapted to engage thetrailing surface of the upper endplate of the prosthetic disc, asdescribed more fully below. In addition, the upper endplate holder 560includes a pair of outer engagement pins 564 extending outward from thefront surface 562, and a center engagement pin 565 also extendingoutward from the front surface. The outer engagement pins 564 and centerengagement pin 565 are each generally cylindrical in shape, andrelatively short in length relative to the size of the push rod 563. Theengagement pins 564, 565 are intended to engage and retain the upperendplate of the prosthetic disc during the implantation procedure, asexplained more fully below.

Turning to FIG. 42, the second chisel 580 includes a generally flatplate portion 583 attached to the end of a push rod 582. One or morewedge-shaped blades 584 attach to and extend upward from the top surfaceof the flat plate portion 583. Similar to the blade 544 of the firstchisel 540, the blades 584 of the second chisel are adapted to creategrooves in the lower surface of the upper vertebra being treated. Theflat plate portion 583 of the second chisel is preferably thicker thanthe flat plate portion 543 of the first chisel 540, and is generallyabout the same thickness as the height of the prosthetic disc. A flange585 extends outward from the bottom of the second chisel 580. The flange585 has a size and is oriented such that it will engage the grooves 506,507 on the guide member 500 during the implantation procedure.

2. Implantation Procedures

a. First Embodiment

A preferred implantation procedure utilizes the spacer 810, chisel 830,and holder 850 shown in FIGS. 36-38. As discussed above, the proceduredescribed herein is in relation to implantation of a one-pieceprosthetic disc. This description is intended to illustrate theapparatus and methods described herein, however, and is not intended tobe limiting.

A first step of the procedure is to expose the two adjacent vertebrae tobe treated by conventional surgical procedures and to remove the naturaldisc. Once the natural disc has been removed, the spacer 810 is advancedand its head portion 816 is placed between the two adjacent vertebrae inorder to separate them. After the vertebrae are adequately separated,the spacer 810 is withdrawn.

The two-sided chisel 830 is then advanced and its head portion 836 isplaced between the vertebral bodies. Because of the size of the headportion 836 relative to the axial space between the vertebrae, thewedge-shaped blades 839 engage the inward-facing surfaces of thevertebrae, creating grooves on those surfaces simultaneously. After thegrooves are formed as needed, the two-sided chisel is withdrawn.

A prosthetic disc is then installed on the distal end of the holder 850.Optimally, the arms 858 a-b of the holder 850 engage the side surfacesof the prosthetic disc, and the proximal side of the disc butts upagainst the distal face of the body portion 857 of the holder 850. Inthis position, the holder is able to retain the prosthetic disc and holdit in place. The prosthetic disc is then advanced by the holder into thedisc space between the two vertebrae. Optimally, the anchoring fins onthe external surfaces of the prosthetic disc are aligned with thegrooves formed in the upper and lower vertebrae as the disc isimplanted. Once the disc has been satisfactorily located, the holder 850is withdrawn, leaving the disc in place.

b. Second Embodiment

An alternative implantation procedure is illustrated in FIGS. 43 through49. The preferred procedure utilizes the implantation tools describedabove in relation to FIGS. 39-42. As discussed above, the proceduredescribed herein is in relation to implantation of a two-pieceprosthetic disc. This description is intended to illustrate theapparatus and methods described herein, however, and is not intended tobe limiting.

Turning first to FIGS. 43A-B, after the two adjacent vertebrae to betreated are exposed by conventional surgical procedures and the naturaldisc is removed, the guide member 500, lower pusher 520, and upperpusher rods 541 a, 541 b are advanced in the direction of arrow “A”toward the void space between the two adjacent vertebrae 601, 602 untilthe outer lower endplate 220 b and first chisel 540 are located betweenthe two adjacent vertebrae 601, 602 (see FIG. 43B).

At this point in the procedure, the distance “d” between the vertebrae601, 602 is insufficient to accommodate the prosthetic disc.Accordingly, as shown in FIGS. 44A-B, a force is applied to separate thefirst chisel 540 and the outer lower endplate 220 b, e.g., asrepresented by arrows “B” in FIGS. 44A-B. The separating force isapplied by advancing the separator 515 away from the base member in theapparatus shown in FIG. 40 by the method described above. The upwardforce by the first chisel 540 causes the wedge-shaped blades 544 of thefirst chisel to embed in the lower surface of the upper vertebra 601,creating grooves in that surface. Similarly, the downward force by thelower endplate insert 523 and outer lower endplate 220 b cause theanchor fins 221 on the lower surface of the outer lower endplate 220 bto embed in the upper surface of the lower vertebra 602. Thus, byadvancing the separator 515 between the upper pusher rods 541 a, 541 band lower pusher rods 521 a, 521 b, the user is able to implant theouter lower endplate 220 b onto the lower vertebra 602 and to create aset of grooves in the upper vertebra 601 that will accommodate theanchoring fins 211 on the upper endplate of the prosthetic disc.

After the separating forces are applied as described above, the firstchisel apparatus is withdrawn, as shown in FIGS. 45A-B. Moreparticularly, the lower pusher 520 is withdrawn, thereby withdrawing thelower endplate insert 523 from the outer lower endplate 220 b, leavingthe outer lower endplate 220 b implanted onto the lower vertebra 602.Also, the upper pusher rods 541 a, 541 b are withdrawn, therebywithdrawing the first chisel 540, leaving one or more grooves formed onthe upper vertebra 601 (see FIG. 45B). The guide member 500 remains inplace to facilitate additional procedures described below.

After the first chisel apparatus is withdrawn, the second chisel 580 isadvanced into the space between the two vertebrae 601, 602, as shown inFIGS. 46A-B. Preferably, the second chisel is advanced (see arrows “A”)into the void space by advancing the push rod 583. Upon entry into thevoid space, the wedge-shaped blades 584 on the top surface of the secondchisel engage the grooves formed in the lower surface of the uppervertebra 601 by the first chisel 540. Advantageously, the flange 585 onthe bottom surface of the second chisel 580 engages and rides in thegrooves 506, 507 on the guide member 500 as the second chisel is beingadvanced, thereby guiding the second chisel 580 into place.

As noted above, the second chisel 580 preferably has a thickness that issimilar to the height of the upper endplate assembly of the two-pieceprosthetic disc. Thus, advancing the second chisel 580 into the voidspace between the two adjacent vertebrae 601, 602 ensures that the voidspace is adequately prepared for implanting the remaining portion of theprosthetic disc. In addition, if the second chisel 580 has a snug fitwithin the void space, this will further confirm that a prosthetic discof the appropriate size and shape is being used.

After the second chisel 580 has been advanced and engages the lowersurface of the upper vertebra 601, it is withdrawn, once again leavingbehind the outer lower endplate 220 b implanted onto the lower vertebra601 and the guide member 500 engaged with the outer lower endplate 220b. (See FIGS. 47A-B).

Once the pair of vertebrae 601, 602 have been adequately prepared forimplantation of the remaining portions of the prosthetic disc, the uppersubassembly 205 of the prosthetic disc is implanted using the upperendplate holder 560. (See FIGS. 48A-B). The upper endplate holder 560 isadvanced in the direction “A” by the push rod 563 until the uppersubassembly 205 engages the outer lower endplate 220 b and is locked inplace by the tab 261 and notch (not shown). At this point, the anchoringfins 211 on the upper subassembly engage the grooves formed on the lowersurface of the upper vertebra 601, thereby helping to retain theprosthetic disc in place between the two adjacent vertebrae 601, 602.Turning to FIGS. 49A-B, the upper endplate holder 560 and the guidemember 500 are then withdrawn, leaving the prosthetic disc in place.FIG. 49A provides additional detail showing the manner by which theengagement pins 564, 565 of the upper endplate holder engages a set ofmating holes 206 formed in the trailing edge of the upper subassembly205. Similarly, FIG. 49A shows the manner by which the lower endplaterods 508, 509 engage the mating holes 215 formed on the trailing edge ofthe outer lower endplate 220 b.

In an alternative method particularly adapted for implanting theone-piece structure prosthetic discs 100 described herein, implantationof the prosthetic disc is achieved without using the guide member 500,through use of only the second chisel 580, the spacer tool 570, and amodified upper endplate holder 560′. The spacer tool 570 is used, asdescribed above, to separate the adjacent vertebral bodies to providespace for the prosthetic disc. The second chisel 580 is also used in themanner described above to provide grooves on the internal surface of thevertebral bodies to accommodate the fins on the prosthetic disc. Themodified upper endplate holder 560′ has a similar structure to theendplate holder 560 shown in FIG. 41, but is provided with an additionalset of engagement pins 564′, 565′ for engaging mating holes provided onthe lower endplate 120 of the one-piece prosthetic disc 100. Themodified upper endplate holder 560′ is used to advance the prostheticdisc 100 into place between the adjacent vertebrae, then is withdrawn.

B. Minimally Invasive Implantation

A minimally invasive surgical implantation method is illustrated in FIG.51. The minimally invasive surgical implantation method may be performedusing a posterior approach, rather than the anterior approach used forconventional lumbar disc replacement surgery.

Turning to FIG. 51, the a pair of cannulas 700 are inserted posteriorlyto provide access to the spinal column. More particularly, an smallincision is made and a pair of access windows are created through thelamina 610 of one of the vertebrae on each side of the vertebral canalto access the natural vertebral disc to be replaced. The spinal cord 605and nerve roots 606 are avoided or mobilized to provide access. Onceaccess is obtained, each of the cannulas 700 is inserted. The cannulas700 may be used to remove the natural disc by conventional means.Alternatively, the natural disc may have already been removed by othermeans prior to insertion of the cannulas.

Once the natural disc has been removed and the cannulas 700 located inplace, a pair of prosthetic discs are implanted between adjacentvertebral bodies. In the preferred embodiment, the prosthetic discs havea shape and size adapted for the minimally invasive procedure, such asthe elongated one-piece prosthetic discs 100 described above in relationto FIGS. 50A-B. A prosthetic disc 100 is guided through each of the twocannulas 700 (see arrows “C” in FIG. 51) such that each of theprosthetic discs is implanted between the two adjacent vertebral bodies.In the preferred method, the two prosthetic discs 100 are located sideby side and spaced slightly apart between the two vertebrae. Optionally,prior to implantation, grooves are created on the internal surfaces ofone or both of the vertebral bodies in order to engage anchoring finslocated on the prosthetic discs 100. The grooves may be created using achisel tool adapted for use with the minimally invasive procedure.

Optionally, a third prosthetic disc may be implanted using the methodsdescribed above. The third prosthetic disc is preferably implanted at acenter point, between the two prosthetic discs 100 shown in FIG. 51. Thethird disc would be implanted prior to the two discs shown in theFigure. Preferably, the disc would be implanted by way of either one ofthe cannulas, then rotated by 90.degree. to its final load bearingposition between the other two prosthetic discs. The first twoprosthetic discs 100 would then be implanted using the method describedabove.

An alternative minimally invasive implantation method and apparatus isillustrated schematically in FIGS. 52A-B. In this alternativeimplantation method, a single cannula 700 is used. The cannula isinserted on one side of the vertebral canal in the manner describedabove. Once the cannula is inserted, a chisel is used to create a groove701 having a 90.degree. bend on the interior surfaces of the twoadjacent vertebral bodies. Thus, the terminal portion of the groove 702is perpendicular to the axis defined by the insertion cannula 700.

Turning to FIG. 52B, a dual prosthetic disc 710 structure is shown. Thedual disc 710 includes a pair of one-piece structure prosthetic discs100 a-b identical in structure to those described above in relation toFIGS. 50A-B. The two prosthetic discs 100 a-b of the dual disc 710 arejoined by a separating mechanism 711. The separating mechanism 711 isaccessed remotely by the surgeon after the dual disc 710 has beenimplanted into a patient's spinal column, and is adapted to drive thetwo prosthetic discs 100 a-b apart once they are implanted. Theseparating mechanism 711 may be a screw device such as a worm screw, aratcheting mechanism, a spring, or any other mechanism suitable forproviding the capability of applying a separating force between the twoprosthetic discs 100 a-b of the dual disc 710. Preferably, an anchoringfin 111 is provided on only one of the prosthetic discs 100 a. Thus,when the dual disc 710 is implanted, the anchoring fin 111 of the firstprosthetic disc 100 a will retain the first disc 100 a in place whilethe ratcheting mechanism 711 causes the second disc 100 b to beseparated spatially from the first disc 100 a, as shown by the arrow“D”.

The subject devices and systems may be provided in the form of a kit forperforming the methods of the present invention. The kits may includeinstructions for using the various devices and systems.

Part C

I. Information Concerning the Descriptions Contained Herein

It is to be understood that the inventions that are the subject of thispatent application are not limited to the particular embodimentsdescribed, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the present invention will be limited only by the appendedclaims.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which these inventions belong. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present inventions, the preferredmethods and materials are herein described.

All patents, patent applications, and other publications mentionedherein are hereby incorporated herein by reference in their entireties.The patents, applications, and publications discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the present invention is not entitled to antedate such publicationby virtue of prior invention. Further, the dates of publication providedmay be different from the actual publication dates which may need to beindependently confirmed.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentinventions.

The preceding merely illustrates the principles of the invention. Itwill be appreciated that those skilled in the art will be able to devisevarious arrangements which, although not explicitly described or shownherein, embody the principles of the invention and are included withinits spirit and scope. Furthermore, all examples and conditional languagerecited herein are principally intended to aid the reader inunderstanding the principles of the invention and the conceptscontributed by the inventors to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the presentinvention, therefore, is not intended to be limited to the exemplaryembodiments shown and described herein. Rather, the scope and spirit ofpresent invention is embodied by the appended claims.

1. A prosthetic intervertebral disc comprising: a first substantiallyrigid, physiologically acceptable end plate, a second substantiallyrigid, physiologically acceptable end plate, a compressible core memberpositioned between said first and second end plates, said core membercomprising at least one fiber extending between and engaged with saidfirst and second end plates.
 2. The prosthetic intervertebral disc ofclaim 1 wherein said at least one fiber extends through said first endplate and through said second end plate.
 3. The prostheticintervertebral disc of claim 2 wherein said at least one fiber extendingthrough said first end plate and through said second end plate is asingle fiber.
 4. The prosthetic intervertebral disc of claim 1 whereinsaid at least one fiber is oblique to said first end plate and saidsecond end plate.
 5. The prosthetic intervertebral disc of claim 1wherein the core member and the at least one fiber extending between andengaged with said first and second end plates are configured to permitrelative rotation of said first end plate relative to said second end.6. The prosthetic intervertebral disc of claim 1 wherein the first endplate comprises a material is selected from the group consisting oftitanium, titanium alloys, stainless steel, cobalt/chromium, ultrahighmolecular weight polyethylene (UHMW-PE), polyetheretherketone (PEEK),ceramics, and graphite.
 7. The prosthetic intervertebral disc of claim 1wherein the second end plate comprises a material is selected from thegroup consisting of titanium, titanium alloys, stainless steel,cobalt/chromium, ultrahigh molecular weight polyethylene (UHMW-PE),polyetheretherketone (PEEK), ceramics, and graphite.
 8. The prostheticintervertebral disc of claim 1 further comprising a plurality of fibers,wherein each of said plurality of fibers extends through said first endplate and through said second end plate.
 9. The prostheticintervertebral disc of claim 8 wherein said plurality of fibers definetwo or more layers of fibers of said core member.
 10. The prostheticintervertebral disc of claim 9 wherein two or more different fibersdefine the two or more layers of fibers of said core member.
 11. Theprosthetic intervertebral disc of claim 8 wherein each of said pluralityof fibers defines a layer of fibers of said core member.
 12. Theprosthetic intervertebral disc of claim 8 wherein the fibers of a firstlayer and the fibers of a second layer exhibit the same tension.
 13. Theprosthetic intervertebral disc of claim 8 wherein the fibers of a firstlayer and the fibers of a second layer exhibit different tensions. 14.The prosthetic intervertebral disc of claim 8 wherein said fibers of afirst layer extend at a first angle and said fibers of a second layerextend at a second angle, wherein said first angle is different thansaid second angle.
 15. The prosthetic intervertebral disc of claim 1wherein at least one of said at least one fibers comprises a memberselected from the group consisting of elastomers, metals, and polymersand said at least one of said at least one fibers is further is selectedfrom multifilament fibers, monofilament fibers, and encapsulated fibers.